Aimed at the problem that the serious wear of the friction pair consisted of cylinder and crankshaft will influence the performance and lifetime of the low speed high torque hydraulic motor,according to the film theory of friction pairs,the reason that the friction pairs of this kind of motors is easily to be worn under high speed low load conditions was theoretically analyzed,and the factors were found out that impacting the bearing friction capability and stability of the friction pair oil film.The results show that it is helpful to improve bearing capability of oil film by increasing the range of opening angle of friction pairs properly.The hydraulic motor can run stably under the condition of low speed,when the rotation speed is higher,due to obvious shearing flow effect,the bearing capacity of oil film at the side of friction pairs is decreased at some extend,which is harmful to stable running of the friction pairs.In a certain range,the larger the hydraulic pressure,the higher is the response sensitivity of oil film system.The high running speed of motor is helpful to the normal running of the friction pairs system.