Abstract: The paper analyzed the moist role in the outburst prevention of outburst seam, had an experiment study on the moist mechanics feature variation law of outburst seam and the water content of seam affected to Protodyakonov cofficient and the initial gas emission speed.The experiment study showed that Protodyakono V coefficient of coal was increased with the water content of coal increased and there was a linear variation relationship between Protodyakonov coefficient and the wat er content.With the water content of coal increased, the gas initial emission speed of coal would be reduce rapidly and there was an approximate index variation law bet ween the water content and the gas initial emission speed.A site investigation was conducted on the gas emission law of coal wall and the outburst prevention effect of outburst seam during the moist process of seam.The results showed that with the water injection and moist of coal conducted, the geostress was evenly distributed, the plasticity of coal was increased, the fragility was reduced, the gas content of seam and the gas pressure gradient was reduced, the gas desorption speed was reduced and the outburst danger of seam was highly reduced.