Abstract: Rainfall humidification causes large deformation or damage to Chengdu clay pit slope. Methods of model test, field test and numerical simulation are used to analysis infiltration depth under different rainfall conditions. Infiltration law and infiltration depth empirical formula are obtained by comparing the results of the analysis. The results show that model test is difficult to simulate really due to Chengdu clay swelling, soil structure and microcracks having a big influence on seepage. The results need a correction through field test. The main factor which influences the rainfall duration is the depth of infiltration. With the increase of rainfall time and rainfall intensity,the increasing speed of infiltration depth gradually slows down. It is good to use piecewise linear fitting. The infiltration depth of single rainfall in Chengdu clay slope is less than 1 m.