The deformation of piston skirt directly affects the assembly clearance with cylinder liner and the lubrica-tion state during the engine operation.In this paper,by taking a general aviation two- stroke piston engine as the re-search object,a finite element model describing the piston- piston pin- connecting rod- cylinder liner assembly is con-structed,the deformation of piston skirt under different loads is calculated and discussed,and a second- order dy-namic model is set up to analyze the lateral displacement of the piston.Moreover,the thickness and pressure of thelubricant film between the piston skirt and the cylinder liner are simulated.The results show that (1) the mainthrust plane of the skirt is of a deformation varying with the load; (2) thermal load may result in a skirt expansionand mechanical load may cause an expansion of the skirt upper end as well as a contraction of the lower end of theskirt; (3) under coupled thermal- mechanical load,the deformation of the skirt is not the sum of the deformationsrespectively under thermal and mechanical loads but varies complicatedly; and (4) during the operation of the en-gine,a wedge- shaped space may occur between the ends of the piston skirt and the wall of the cylinder liner,whichmakes the appearance of film lubrication between the piston skirt and the cylinder liner possible.