Cutting unit reducer is a very important part of roadheader, its performance greatly affected roadheader. Due to the narrow underground roadway working space, the shape of the device is required to minimize, EBZ-135 roadheader planetary gear unit volume was optimized by volume reducer function to identify the relevant constraints, using MATLAB calculation optimization. The results showed that in the first stage of the optimized tooth thickness decreased by 14.5%, the first stage gear modulus decreased of 43.6%, volume reduction gear about 22.3%, and optimization effect was good. In addition, the use of MATLAB to optimize the design, greatly improved the optimization of efficiency and reduced the workload of the technical staff.