A multi-body dynamic force calculation method was proposed to deal with the difficulty of accurate force calculation due to the complicated and time-varying characteristics of crank arm bearing force． This method was fur-ther employed to analyze the influence patterns of input speed and load condition on the force of the rotating arm bearing． The results indicate that the force of the arm bearing changes cyclically with the crank angle，and the rota-tion speed has no influence on the extreme value of the arm bearing force but has effects on its fatigue life． The force of the rotating arm bearing increases as the load increases． In addition，the comparision between the result of geometric analysis and that of the proposed algorithm suggests a good consistency between the two． Based on these results，the finite element method was further used to analyze the influence of different working loads on the contact stress of the rotating arm bearings． The results show that there is a single-sided force phenomenon in the arm bea-ring，and the contact stress of each needle is different from each other． These findings provide a theoretical basis for engineering application and optimization analysis of rotating arm bearings．