Abstract: In order to study reliability of planetary reducer of shearer cutting unit under influence of multiple factors, taking the MG400/951-WD shearer as research object, the load curve of spiral drum is calculated according to force analysis of pick and measurement result of coal sample mechanical properties. The load is applied to the model of cutting unit for simulation, and stress information of planet carrier and planet shaft is obtained. The reliability information of planet carrier and planet shaft is obtained by building a stress-reliability Gaussian membership function. Based on orthogonal test, influence law and significance degree of Protodyakonov coefficient of coal, traction speed of shearer and cutting depth of spiral drum on reliability of planetary reducer are analyzed. It is concluded that traction speed of shearer has the greatest influence on the reliability of planetary reducer, followed by Protodyakonov coefficient of coal, and the cutting depth has the least influence on the reliability of planetary reducer. With the increase of the Protodyakonov coefficient of coal, the decrease of the reliability of planetary reducer increases, and the decrease trend of the reliability becomes more obvious. With the increase of traction speed and cutting depth, the decrease of planetary reducer reliability tends to be gentle.