The pot experiment was conducted on the effect of soil moisture on yield of cucumber and soil microbe in a greenhouse. The results show: (1) The number of soil microbe is different in the treatment of soil moisture of cucumber. The number of bacterial in soil is the highest when soil moisture is 80%~90% field water capacity in florescent stage. The number of bacterial in soil increases when soil moisture is from low to high and decreases when soil moisture is from high to low in early-fruit stage and fruit stage. The number of bacterial in soil increases when soil moisture is from low to high and decreases when soil moisture is stable or from high to middle or from low to middle in early-fruit stage and fruit stage. The number of fungi in soil increases when soil moisture is stable or low and decreases when soil moisture is not stable or high. The number of actinomycete in soil is fewer difference in florescent stage and early-fruit stage. The number of actinomycete in soil increases in fruit stage and decreases in late-fruit stage. (2) The yield of cucumber is the highest by 389.65g / plant when soil relative moisture is 80%~90% field water capacity in florescent stage and early-fruit stage, 90%~100% field water capacity in fruit stage and 70%~80% field water capacity in late-fruit stage. Its increased yield is 27.74%、18.21%、12.51% than 70%~80% field water capacity and 80%~90% field water capacity and 90%~100% field water capacity in procreation stage.