Geothermal survey is an important tool in petroleum exploration. Among the geothermal parameters, the geothermal gradient is more often used by petroleum geologist because the hydrocarbon generation of source rocks is directly associated with temperature. However, the measured geothermal gradient data originated from diverse depth range, make spatial comparison a challenging task. In the conventional study of geothermal field of sedimentary basins unfortunately, the fact that geothermal gradient is depthdependant is often ignored. A "uniform" geothermal gradient method is brought forward in this paper and a case study is carried out in order to demonstrate the necessity of this method in studying the spatial distribution of geothermal gradient of sedimentary basins.