Abstract: The present invention provides a method and an apparatus for determining an oil-gas-water interface based on the formation pressure equivalent density. The method comprises determining working parameters of the wireline modular formation tester based on the acquired conventional logging data of a block to be studied; acquiring a series of formation pressure and corresponding depth data based on the working parameter; computing formation pressure equivalent densities at different depths based on the formation pressure and the corresponding depth data; drawing a crossplot of the formation pressure equivalent density and the depth according to the formation pressure equivalent density and the corresponding depth data at the different depths; and determining the oil-gas-water interface according to the position of breaking point of the formation pressure equivalent density on the crossplot of the formation pressure equivalent density and the depth.