In order to ensure a three-dimensional horizontal well to be drilled to the geological target safely and efficiently, the optimal design and research on trajectory of three-dimensional horizontal well was made by using COMPASS software. The design rules for the pre-target displacement of three-dimensional horizontal wells have been concluded by computer simulation study. The minimum longitudinal pre-target displacement was put forward. These provide the basis for the optimal design of the pre-target displacement of 3-D horizontal wells.