Abstract: The infiltration of water through wall cake pore under the effect of fluid pressure is the cause of instability of water sensitive formations during drilling process. In order to better understand the laws of infiltration, infiltration test is conducted under different fluid pressures. The test results show that when infiltration time is the same, the infiltration water increases first and then decreases with increasing of fluid pressure. When fluid pressure is the same, the infiltration rate decreases with increasing of time and eventually tends to a stable value. The stable value of infiltration rate has a low correlation with fluid pressure. When fluid pressure is different, the proportion of previous infiltration volume and the cake mass(under dry conditions) increase with increasing of fluid pressure. Infiltration of water increases first and then decreases with increasing of cake mass. The results of the test can provide reference for evaluation and control of fluid infiltration.