For adapting to high speed development of the rotating machinery, the dynamic simulation was studied based on a box of certain typed reducer. The rotational speed and output loads of the reducer were simulated by step function, and dynamic simulation and loads calculation of the reducer were done in environment of ADAMS/View. Finite element model of the reducer box was set up by ANSYS platform, and harmonic response analysis of the box was carried out on the basis of its modal analysis, thus then curves such as amplitude-frequency response, stress-frequency response from 45 Hz to 115 Hz were acquired, and the results of the harmonic response was verified analysis which combined with some key modal frequencies and vibration modes. All of above provided some important basis for structure design and dynamic optimization of support parts in box type.