Based on the dimensional unity, analyzed mechanics, adsorption, desorption and seepage characteristics in the process of outburst by equation analysis method. Combining the existing experimental condition, proposed similarity model which could be more similar to practice and theory, and researched scale effect of outburst physical simulation. Analyzed the geometry size influences release area size, elastic energy, gas energy, broken power and throwing power in the process of outburst. Improved similar material of coal and gas outburst, considering seepage characteristic. The results show that realizing the consistency of the stress ratio scale and the gas pressure ratio is the key in the outburst similarity model. Scale effect plays an important role in the occurrence and development of outburst. In terms of energy contribution, gas can contribute more energy to outburst than elastic energy. Refer to energy dissipation, broken work is more than 95 % in outburst energy, and throwing work is only a small part in outburst energy.