Abstract: In order to rationally develop and utilize the water resources, improve the utilization efficiency of water resources in semi-arid, to provide more fine services for modern agriculture development, based on the study of relationships and characteristics between soil moisture and precipitation in Fuxin to identify Fuxin Region variation of soil moisture, and on this basis, the assessment technology of Fuxin farmland drought water were established. The results showed that: (1) after greater rainfall, shallow soil moisture increased rapidly, soil moisture could reached the maximum within a few hours, and a high aquifer was formed about 20 cm; deep soil moisture was relatively growth slowly, soil moisture reached to a maximum in twenty hours; (2) greater precipitation occurred a day after, 10-50cm layer of soil moisture by weight maximum, then in the absence of precipitation soil moisture content reduced slowly, substantially linear, until the arrival of the next strong rainfall, soil moisture to rise again; (3) affected by many factors, after precipitation, the increased rate of each day soil moisture at 10-50 cm layer and under fine weather, the lapse rate of each day soil moisture had its own variation. Among them, the increased rate of each day soil moisture was relatively small increase in moisture in April, July, September was biggest, in August, followed by; April, May daily soil moisture lapse rate minimum, June to September was relatively large, which, in July the largest. Soil moisture lapse rate in drought water demand calculation played an important role; (4) drought water demand was greater than the actual moisture content of the required set weight water content, soil evaporation due to be considered, crop uptake, deep penetration, precipitation runoff water loss; (5) drought water demand assessment methods of the government decision-making meteorological services played an important role, and could be used for natural precipitation analysis for drought mitigation, water-saving irrigation work fine weather services.