Abstract: A large amount of gas rapidly released during coal and gas outburst is an important cause of dynamic effects such as outburst shock waves and coal-gas two-phase flow. To clarify the influence mechanism of desorbed gas on outburst dynamic effects, physical simulation tests of outburst dynamic effects under different gas pressures and adsorbed/non- adsorbed gas conditions were carried out. The influence of gas on the characteristic parameters of outburst shock waves and the migration of coal-gas two-phase flow was analyzed. The concept of “gas desorption equivalent particle size” was defined to reflect the gas desorption rate of the outburst crushed coal particle group. Combined with gas diffusion dynamics theory, a model of initial desorbed gas expansion energy of outburst coal was constructed, and the action mechanism of desorbed gas was discussed from the perspective of energy sources. The results show that due to the extremely short formation time of the outburst shock wave (several milliseconds), the desorbed gas in coal has a limited influence on the shock wave. The gas pressure has a significant influence on the outburst shock wave; as the gas pressure increases, the peak overpressure gradually increases, and its attenuation along the roadway tends to increase. The outburst intensity increases with the increase of gas pressure and gas adsorption capacity; under CO₂ test conditions, the mass of outburst coal is 1.4 times that under helium test conditions. The energy dissipation of outburst dynamic effects is divided into crushing work, throwing work, and energy dissipated by the outburst shock wave. Under low gas pressure conditions, energy dissipation is dominated by crushing work (accounting for 73.9% at 0.3 MPa). With the increase of gas pressure and adsorption capacity, the proportion of throwing work gradually increases, while the proportion of energy dissipated by the outburst shock wave is basically less than 10%. The energy contribution rate of desorbed gas from outburst coal to the work done by outburst dynamic effects ranges from 33% to 90%, increasing with the increase of gas pressure and gas adsorption performance. A model of initial desorbed gas expansion energy from crushed coal based on the concept of gas desorption equivalent particle size was established. The calculation results of the model show that the desorbed gas expansion energy of outburst coal during the outburst process is fully involved in the work done by outburst dynamic effects. The influence of different factors on the desorbed gas expansion energy of outburst coal was discussed: the gas desorption equivalent particle size has the most significant influence on the desorbed gas expansion energy of outburst coal. The desorbed gas expansion energy of outburst coal increases slowly with the decrease of equivalent particle size, and increases significantly when the equivalent particle size decreases to 0.5 mm. Thus, stress can also affect the release of gas expansion energy by influencing the degree of coal and rock fragmentation. The desorbed gas expansion energy of outburst coal increases with the increase of adsorbed gas pressure and initial diffusion coefficient, with the increasing amplitude gradually decreasing; it shows an almost linear growth relationship with the increase of gas content.