Abstract: In order to understand the effects of diurnal temperature at seedling stage on the growth, development and yield of tomato plants, experiments were carried out using climate box(SPX-250IC) under the average temperature of 20℃. Diurnal temperature were 0(day temperature and night temperature were 20 and 20℃), 6(day temperature and night temperature were 23 and 17℃)and 12℃(day temperature and night temperature were 26 and 14℃), respectively. Floral bud differentiation, matter accumulation, flowering, fruiting and yield characteristics were studied under 3 DIFs above. The results showed that compared with diurnal temperature of 0，dry matter accumulation of per plant were increased by 48.77%-55.73%, floral bud differentiation was advanced, the number of floral bud was decreased by 17.0%-18.2% on 28th day under diurnal temperature of 12. Though the average time of flowering and fruiting of the first 3 trusses were advanced by 2.3d and 1.9 d after transplantation, yield were decreased by 14.3%-16.3% because of the number of floral bud, flower and fruit were decreased by 9.2%-19.7%, 12.4%-23.3% and 1.5%-30.0%, respectively, and fruit number per plant in the end was decreased by 5.8%-17.0%，fruit mass was decreased by 7.8%-8.3%. However, dry matter was too lower to gain a sustainable high yield under diurnal temperature of 0. Particularly, dry matter under diurnal temperature of 6℃ was increased significantly compared with diurnal temperature of 0, the number of flower and fruit were increased, and fruit matter and yield were increased significantly compared with diurnal temperature of 12℃. As a whole, it was conclusion that diurnal temperature of 6℃ was the point of the balance among the dry matter accumulation, floral bud differentiation and post-production, which was benefit for the growth and the production of tomato plants. This research provides a reference for the control of temperature in raising seedlings of tomato plants.