Abstract: In order to compute the load capacity of asperities for Piston ring-cylinder liner in internal combustion engine at running-in stage , the load capacity equation of asperities , including load capacity of elastic deformation and Plastic deformation asperities , was derived from the contact model of rough surfaces . And the equation was compared with the load capacity equation traditionally with the assumption that all of the contact asperities have elastic deformation . The results showed that , the load capacity of contact asperities can be calculated with the assumption that all of the contact asperities have elastic deformation in the middle or later running-in stage when h/σ>0.5andψ<0.9 . While at the initial running-in stage when h/σ<0.5andψ >0.9 , the load capacity of contact asperities with the assumption that all of the contact asperities had elastic deformation was about 50 % - 85 % of the situation that the contact asperities had elastic as well as Plastic deformation . In the light of the importance of the initial stage during running-in for Piston ring-cylinder liner , the load capacity of elastic deformation and Plastic deformation asperities should be studied independently when calculated the load capacity of asperities , which showed that the established equation could be more accurate for tribological conditions analysis of Piston ring-cyhnder hner during running-in .