Abstract: Abstract: Planting and transplanting technology of rice seedling nurturing in hole tray is a high and stable yield cultivation technique in cold weather ecological conditions in China, and a lot of practical productions have proved that the technology has increased production significantly in the northeastern areas, especially in Heilongjiang Province. For cultivating the seedlings with the best quality, some existing experimental studies indicated that the ideal sowing amount of the normal japonica rice (Kongyu 131, Longging 26 and Long yang 16 ) was 40-55 g in each 448-cell potted tray, and on average, there were only 2-3 bud seeds per hole. To improve the precision of seeding (2-3 bud seeds per hole) of japonica rice seedling nurturing in hole tray and promote the extension and application of this technique in large areas in north cold rice-growing areas, based on the analysis of development of the air-suction drum-type seed-metering device with auto-cleaning block, the structure of seed box was improved to improve seed-group structure and the liquidity of seeds in the seed room, a new cleaning-seed mechanism was added for raising the seeding precision, and a replenishing place was designed, which was between the 2 seed-cleaning mechanisms aimed at enhancing the filling seed effect. The ranges of the key structure parameters and working parameters of the improved device were defined. According to the pre-experiments and date commonly used in production, opening width of the seed-box, seed-cleaning gap, rolling brush speed and vacuum degree were the main impact factors of the improved device's seeding performance. On the test equipment of self-developed air-suction drum-type seed metering device, whose seeding productivity was 450 trays (448-cell potted tray) per hour, the japonica rice bud seed Kongyu 131 was selected as experimental material, which had been pre-germinated under the moisture content of 22.34%-23.26% (wet basis). Its bud length was less than 1 mm, and the overall dimensions of clustered area of the seeds were as follows: length of 6.74-7.21 mm, width of 3.34-3.72 mm and thickness of 2.20-2.57 mm. And the effects of the 4 main impact factors on missed seed rate (no bud seeds per hole), 1-4 seeds rate (1-4 bud seeds per hole), 2-3 seeds rate (2-3 bud seeds per hole) and damage rate of seeding were studied by four-factor and three-level orthogonal experimental design. The results of orthogonal experiment showed that the order affecting the missed seed rate, 1-4 seeds rate, 2-3 seeds rate and damage rate was seed-cleaning gap > opening width of the seed-box > vacuum degree > rolling brush speed, and the optimal combination parameters were that the opening width of the seed-box was 40 mm, the vacuum degree of suction chamber was 5 kPa, the rolling brush speed was 55 r/min and the seed-cleaning gap was 6 mm; the probability of 2-3 seeds per hole was 83.23%, and the missed seed rate and damage rate were 1.09% and 0.14%, respectively. In addition, the performance contrast test was carried out under the same conditions with 3 kinds of japonica rice bud seeds (Kongyu 131 and Longjing 26 with the similar overall dimensions, and Longyang 16 with some differences from the above) using the air-suction drum-type seed metering device before and after improvement. The experimental results showed that the improved device had a good adaptability for seeding Kongyu 131 and Longjing 26 with the similar size. Compared with the primary metering device, the probability of 2-3 seeds per hole increased by about 3.77 and 6.14 percent point, respectively, the damage rate decreased by about 5.73 and 6.44 percent point, respectively, and the missed seed rate decreased by about 0.51 and 0.57 percent point, respectively. The research further indicated that improving the fluidity of the bud seeds and decreasing the friction force and extrusion force among the seeds not only could decrease the damage rate effectively, but also may increase the probability of 2-3 seeds per hole and meet the seeding requirements of japonica rice seedling nurturing in hole tray. The study provides an important reference for the structure optimization and the seeding performance further improvement of the suction metering device for rice seedling nurturing in hole tray.