Abstract: The ridge and furrow micro-water harvesting(RFMH) system was developed by scientists in Gansu Province over a decade ago, which was designed to increase water available for crops for higher and more stable agricultural yield on rainfed lands under semiarid condition. In the experiment there are three ridge-furrow ratios and two pad materials. The ridges covered with plastic film and ridges compacted with soil serve as rainfall harvesting zones, and furrows serve as planting zones. The field experiment(potato as an indicator crop, because potato is popular and suitable in the study region) was conducted to determine the effects of different ridge-furrow ratios and different pad materials on tuber yield and water use efficiency(WUE) in the RFMH system during the growing seasons of 2001 and 2002.The experimental results showed that the ridge-furrow ratio and pad material had significant effects on tuber yields and WUE. The WUEs in ridges covered with plastic film were 2.8 times as high as that of the controls in 2001 and 2.4 times in 2002, respectively. No differences were found in WUE between ridges compacted with soil and controls. Although the tuber yields are different because of precipitation in 2001 and 2002, the increases of tuber yields have the similar tendency. On the average the tuber yields in ridges covered with plastic film increased by 231% in 2001 and by 153% in 2002 compared with those of the controls, and the tuber yields in the ridges compacted with soil increased by 58% in 2001 and by 23% in 2002 compared with those of the controls. By straight line regression analysis, the optimum ridge-furrow ratios for ridges covered with plastic film were 60 cm∶41 cm in 2001 and 60 cm∶39 cm in 2002, respectively. Through two years' field experiments, the optimum ridge-to-furrow ratio was 60 cm∶40 cm for plastic-covered ridge in the semiarid areas in Loess Plateau of Northwest China.