Abstract: Laser drilling is a highly efficient, clean and controble new drilling technology, has great potential in CBM development. From the process of breaking coal and rock by laser and circulating gas, the paper analyzed theoretically the action process of breaking coal and rock by laser, took the average power density and the time of laser irridiation on coal and rock surface as variables, air and nitrogen as circulating medium, conducted experiment of breaking coal and rock by laser. The experiment results were basically consitent with the theoretical analysis, showing concretely that within limits increasing the average power density and the time of laser irridiation would make the drilling footage and the borehole diameter as well as the heat-affected zone increase, which is favorable to enhance the drilling efficiency of breaking coal and rock by laser, while circulation of nitrogen and air for breaking coal and rock by laser each has advantages, and alternate circulation drilling can be conducted.