In order to have a theoretical design basis for the size design of inlet section of plunger pump,the flow rate and resistance along the path of grease under different size conditions of pipeline were calculated.According to the theory of rheology and fluid mechanics,flow state of grease in pipeline was analyzed,the flow equation of grease in inlet section was derived,and critical conditions of laminar flow of grease pipeline were determined.The results show that for the studied plunger pump,the flow rate decreases sharply when the length of the inlet section increases from 0 to 15 mm,and the flow rate is relatively stable when the length is greater than 15 mm.The flow rate shows a gradual increase when the radius increases from 0 to 30 mm,and sharply increases when the radius exceeds 30 mm.The results of finite element simulation are consistent with those of numerical analysis,and have similar variation rules,which proves the accuracy of pipeline flow equation.Therefore,the derived flow equation of grease in pipeline is applicable to the engineering design of lubrication pumps.