To improve the coldstart friction state of cylinderpiston ring and reduce friction power loss,the variation of coldstart lubrication state and friction properties of pistoncylinder at different ambient temperature was studied by establishing the mathematical model of piston ringcylinder friction under mixed lubrication state.The variation curves of coldstart friction of piston ringcylinder was obtained for a diesel engine,and a model was proposed to predict the piston ringcylinder liner friction varies with temperature.The results show that,with the decrease in ambient temperature,the average friction of cylinderpiston ring is increased slightly,while the maximum friction has a great increment.The mathematical model of piston ringcylinder friction was simulated.The error between the simulation results and the prediction results by the model of piston ringcylinder friction temperature change effects is less than 8.526%,which verifies the reliability of the mathematical model of maximum frictional force.