The mechanical properties of loaded coal time to time, so that the voice wave propagation in coal changes with it. In order to study the relationship between the wave velocity of coal and its mechanical properties.The ultrasonic testing system was used to calculate the wave velocity of loaded coal at different times through laboratory triaxial loading test.The relationship between the wave velocity of loaded coal-body and the confining pressure of different coaxial pressures was analyzed.The results show that the wave velocity is positively correlated with the axial pressure under the same confining pressure. By calculating the variation of wave velocity of different loaded coal bodies. it is concluded that the variation of wave velocity of coal bodies can reflect the mechanical state of coal bodies undergo the compaction stage, the elastic stage and the new stage of crevasse. At the same time, the change of wave velocity in coal is affected by the porosity of the pressure-bearing coal-boby. Porosity was calculated using stress-strain.It was found that porosity and axial pressure presented a good negative correlation under the same confining pressure, and the change in wave velocity is exactly right opposite to the porosity change trend diagram.It can be obtained that the larger the amplitude of wave velocity change is, the smaller the porosity change is, and the smaller the amplitude of wave velocity change is, the larger the porosity change of coal body is, which is consistent with the actual analysis. It verifies the different the pressure-bearing coal-boby change in wave velocity to the feasibility of analyzing the mechanical condition of the loaded coal body. making the analysis more persuasive. It provides basis for coal body bearing and safe mining.