Cutting arms are the main productive units of coal shearer machine that contact directly with coal seam. More importantly, the cutting arms operate under a high stress environment. In this paper, in order to suggest an optimum maintenance plan for the subsystem of shearer machine, firstly, we conducted a failure and reliability analysis using the data acquired from the Parvadeh coal mine Iran over the last two years. In doing so, we applied estimated distribution functions and calculated cost parameters to identify the cost-based optimum preventive maintenance interval. The analysis shows that the Power Law Process model provides a good fit to the failure data. Accordingly, the preventive maintenance operation can improve the reliability of the system by 53.5%. Furthermore, we conducted a sensitivity analysis of the studied machine and identified that if we consider the variation of the world price of the raw coal then the maintenance plan is sensitive to the price, however the effects of this change on reliability improvement is almost zero