In order to overcome the limitation of ABAQUS in simulation of rainfall infiltration, the paper used Python language to develop the rainfall infiltration boundary of ABAQUS software secondary.It considered the rainfall boundary as an uncertain boundary, used the iterative algorithm to treat the boundary,and developed rainfall modulus. The modulus can change instantaneously rainfall boundary conditions according to the relation between rainfall intensity and infiltration capacity of soil,and thereby reflects the dynamic changing process of the boundary condition in rainfall process,and overcomes the unchanged infiltration rate adopted in ABAQUS, thus improves the analysis function of rainfall infiltration by use of ABAQUS.The results show that the developed rainfall modulus is reasonable can be used in analysis of slope rainfall infiltration; meanwhile, by the aid of the powerful feature of ABAQUS, this modulus can provide a good research platform for more complicated rainfall problems in the future.