Engine lubrication system model was built with AMESim software, and validated by test data to ensure the model precision( the error is less than 31%). Based on this model, the influence of the clearance of crank main bearing, connecting rod bearing and camshaft bearing on the lubrication system of engine was studied. Simulation result shows that along with the increasing of bearing clearance under the same lubricating oil flow rate, the system oil pressure is decreased. But to different bearings, the extent of oil pressure decrease is different, to difference engine speed, the level of pressure decrease is also different, it is higher at low speed than that at high speed.