After the vehicle diesel engine is converted to nonroad use,the rated power speed is decreased from 3 600 r/min to 2 400 r/min,which puts forward higher requirements for the original oil pump.The one-dimensional simulation model of diesel engine lubrication system was built by AMESim software.The simulation analysis shows that the main oil pressure of the oil pump can not meet the requirements of the new working condition after the rated power speed of the diesel engine is reduced.The rated flow rate of the oil pump and the opening pressure of the relief valve were analyzed and optimized.The maximum rated flow rate and the opening pressure of the oil pump were adjusted from 35.3 L/min and 600 kPa to 50 L/min and 500 kPa without changing other structural parameters.The simulation analysis shows that after optimization,the main oil channel pressure can meet the lubrication requirements of the relevant parts of diesel engine,and the minimum oil film thickness can meet the design requirements.Meanwhile,it is found that the greater of the resistance loss of the oil filter and cooler,the more obvious the decrease of main oil channel pressure,and the outlet pressure of oil pump is increased with the increase of the total resistance of the oil filter and cooler.