Abstract: A field experiment was conducted to study the effects of different compound microbial fertilizers on yield、quality and water use efficiency of potato at rain fed farmland south of Ningxia in 2015. The experiment was made of ‘Zhuang potato No. 3’as the material，To determine the appropriate amount of compound microbial fertilizer.There are 5 treatments in this experiment,farmer conventionl fertilizer treatment（CK）,compound microbial fertilizer 375kg/hm2、750 kg/hm2、1125 kg/hm2、1500 kg/hm2.The results showed that: under the condition of the same amount of conventional fertilizer, increasing compound microorganism fertilizer application rate to improve the plant height, stem diameter and stem number of potato, a significant difference compared with the control (P<0.05). Compound microbial fertilizer increased potato tuber number per plant, yield per plant and medium and large potato percentage. Compared with conventional fertilizer, compound microbial fertilizer increased the contents of reducing sugar, vitamin C, starch and dry matter, and improved the quality of potato. The yield of potato was 1.0%-14.7%, the increase rate of water use efficiency was 4.3%-17.6%. The equation effect of water and fertilizer showed the highest yield or highest water use efficiency of microbial fertilizer amount were 954.8 and 1415 kg/hm2. But the application of 750 kg/hm2 can obtain high yield. So it was proved that reasonable application of compound microorganism fertilizer could be 750-1415 kg/hm2 in the in dryland of southern Ningxia.