Creating a 3D terrain or a wave surface takes a lot of time for a graphic artist in the 3D game creation process. This problem poses the following computer requirements: the generated terrain surface must be both random at all points, but also smooth and curved, and the difference between the vertices must be controlled by the input parameter. This paper will upgrade the Gaussian Process (GP) from 2D to 3D in order to solve this terrain generation problem. In addition, when the generated surface becomes very large, GP requires a large amount of computation related to matrix analysis. This paper proposes an approximate solution to speed up the computation.