[Objective] To analyze the effects of runoff gather engineering on soil moisture conversation in afforestation land converted from cropland in order to provide the basis for improving soil water supply in planted forest.[Methods] With an intensive survey on the runoff gather engineering and afforestation types, we investigated soil moisture conservation and growth and development of tree and grass under different site preparation practices including slope-separate flat terrace(SSFT), slope-separated reversing sloping terrace(SSRST), cone-shape focused fluid pit(CFFP), Swallow-tail-shape focused fluid pit(SFFP) in the region of returning farmland to forest land in Anding district of Dingxi City, Gansu Province.[Results] The runoff gather engineering increased soil moisture and improved water supply to the plants greatly. The total water supply for individual tree reached to 2.54~4.29 m³/a, and it reached to 1.42~1.79 m³/a for an individual bush. Soil moisture within the 2 m soil depth varied from 8.76% to 11.40%, which satisfied the water demand for the growth and development of trees and grasses.[Conclusion] Feasible runoff gather engineering practices combined with suitable tree species, can improve soil water supply in planted forest.