Pit irrigation is a new method that can check soil erosion suitable for fruit tree and forest in gully and hilly. According to the specific of pit irrigation field engineering, the characteristic of runoff producing rain and sink flow in pit irrigation were analyzed. Based on this, the runoff process, initial abstraction time, runoff amount and runoff coefficient in a fruit tree control areas were analyzed and deduced; meanwhile,corresponding theoretical models were worked out; an example of models application was illustrated. This study will have an important value for design on field engineering of pit irrigation under some soil and water conservation standard condition.