Relative permeability is a critical parameter for evaluation of gas reservoir performances. Earlier works have indicated that relative permeabilities are markedly dependent on pore geometry, wettability, fluid saturation, saturation history, reservoir temperature, reservoir pressure, overburden pressure, rock types, porosity and permeability types. Some literatures have reported effect of reservoir temperature, reservoir pressure, overburden pressure on relative permeability. Because we are subjected to experiment conditions, it is very difficult for Dabei naturally fractured gas reservoir to measure relative permeability under 120 MPa abnormal high pressure and 145 Centigrade high temperature. In this paper, relative permeability of 12 cores without fracture and 3 cores with fracture during displacement of water by gas and displacement of gas by water in Dabei naturally fractured gas reservoirs under lower pressure and room temperature was measured. The results indicated that relative permeability in the process of displacement of water by gas is obviously different from that in the process of displacement of gas by water. Gas-water relative permeabilities of rock with fracture are higher than that of rock without fracture. In order to evaluate effect of abnormal high pressure and high temperature on relative permeability. A transformation model of gas-water relative permeability from experiment conditions to reservoir conditions was built up. A high temperature and high pressure wells for example, the effect of temperature and pressure on gas-water permeability was analog calculated, which the result indicated that water relative permeability cannot be effected by temperature and pressure, but gas relative permeability is. While gas relative permeability measured at experiment temperature and pressure which is beyond 10 times difference than the high pressure and high temperature at reservoir condition. It is suggested that it is unadvisable to predict gas reservoir performance by using gas-water relative permeability measured at experiment conditions.