As to the complex situations of the gas drilling process that have influence on the safety of well drilling such as layer watering out, excessive torque and friction or making a trip hard, and the problem that gas drilling had to be converted to the drilling mud to drill, this article bring forward the request of drilling mud performance in the process of mud system transformation, and summarize a feasible measure to solve those problem. That is the shielding temporary plugging technique that the positive differential pressure, a bad factor, can be conformed to the technique in favor of protecting layer. And this article brings forward the applied feasibility in the process of mud system transformation of the ideal backfill theory and d90 temporary plugging theory, the mixed metal layered hydroxide compound drilling fluid system, the mud system transformation ahead fluid and the corresponding drilling fluid system.