To study the dynamic characteristics of planetary reducer mechanism of shearer cutting unit under complex coal seam condition reliability,the shearer rigid- flexible coupling model is established. The analysis and dynamic simulation of the shearer outer drum load under the extreme condition are carried out,and the load and virtual simulation is carried out in the dynamic simulation software Recur Dyn. Through the force analysis of the inner gear ring in the cutting unit planetary reducer mechanism,the maximum equivalent stress location is found out and according to its force condition,the structure optimization is carried out. Through the simulation for the planetary reduction mechanism after gear modification,it is found that the maximum equivalent stress is less than the material allowable stress,and the tooth surface fatigue life is greatly improved. An important reference for the study on gear dynamics is provided.