Under air pressure, air inflow is the starting point for the failure of filter cake. In order to measure and study airentry value(AEV) of filter cake under air pressure, through selfmade test device, the measurement of the AEV of three kinds of filter cakes under different pressure conditions is carried out. The results show that: (1) The difference value between airclosed draining and consolidation drainage can be used to distinguish whether air inflow happens or not, and AEV of filter cake can be obtained.(2) AEV can be approximately calculated by substituting the characteristic pore diameter D90/2 into the derivation formula. (3) AEV of filter cake is different under different air pressure conditions, the lower the rate of pressurization, the larger the AEV is. (4)The change of AEV at a faster and slower rate of pressurization rate tends to be stable, the maximum AEV is more than two times the minimum.