Either success or failure of natural gas exploration depends on enclosed system or escaped system of the gas reservoir trap. Whether the enclosed system of a trap is good or poor lies on available enclosed surface of the trap and the effective sealing condition of the whole overlying regional cap rock with the circumstance condition of regional hydrodynamic stagnation zone. Available traps with good enclosed surfaces mean high rate of successful exploration. An escaped system of a gas reservoir trap includes denuded area without effective sealing condition of regional cap rock, the circumstance condition of regional hydrodynamic free alternation zone, and obvious and/or hidden faults extending to the surface. An escaped system will lead to an invalid gas trap, which means failure of exploration. By case analysis of wreck and preservation conditions of gas reservoirs in Sichuan Basin, it is suggested that an attention should be paid to the studies of wreck and preservation conditions of gas reservoirs in natural gas exploration in Sichuan Basin and southern China to achieve exactly choice aims of exploration and rise exploration efficiency.