A dimethyl ether(DME) engine was developed with a modified fuel supply and injection system based on a WEICHAI WP6 Diesel engine.The combustion parameter of DME engine was acquired by experiments,and a numerical model for piston dynamics and lubrication analysis was proposed by coupling the dynamics model of multibody system consisting of piston,crank and connecting rod,and the lubrication model of piston skirtliner system.The lubrication model was solved with finite element method (FEM),while the multibody dynamics equations were established with Lagrange multipliers.The coupling calculation results were compared with experimental ones,and the accuracy of the model was verified.Based on the present piston skirt structure,some structure parameters of piston skirt were investigated so as to reveal their effect on the slap noise and lubrication performances of the piston.The results show that,the smaller the clearance of piston,the smaller the space of secondary motion of piston,which will decrease the slap noise of piston and reduce the wear.However small piston clearance will produce higher shearing force of oil film,and aggravate surface contact of asperity,leading to larger friction force and power consumption.Barrel peak position of piston skirt will also affect the characteristics of lubrication and motion of the piston skirtcylinder system.When the distance between barrel surface and piston pin center is smaller,the balance condition of force and torque is more easy to be satisfied,which is helpful for reducing slap noise and friction power consumption.