Using TGA technology, the volatile matter yields during hydropyrolysis of Chinese Shenmu coal and its derived high purity macerals under different heating rates and pressures were investigated. The Delta W, calculated by the difference between the volatile matter yield of parent coal and that of macerals, is used to evaluate the synergistic effect of macerals during hydropyrolysis. The results showed that with increasing pressure and decreasing heating rate, the Delta W increases. At temperature of 500 degrees C and pressure of 3 MPa, the difference of volatile matter yield between parent coal and vitrinite reaches the maximum and the Delta W also occurs the highest value of 14.1%, suggesting the existence of the synergistic effect between macerals during hydropyrolysis. Based on the structural characteristics of macerals and the basic knowledge of hydropyrolysis, the possible explanation for the synergism are proposed.