Abstract：During modeling numerical simulation by FLAC3D, the three-dimensional numerical model is accurate or not is the key factor to predict the accurate results.In order to establish a precise three-dimensional numerical model, the paper proposes two kinds of establishing three-dimensional numerical model.Method 1 is that model three-dimensional numerical model by surface fitting, the method has several advantages that is fast modeling and easy to write general program.But when the terrain is not expressed by the space curved surface, method 1 does not apply.Method 2 for the cubic spline interpolation to establish three-dimensional numerical model, this method can be used to established three-dimensional numerical model of the space of any shape.But this method has the following disadvantages: the pre-treatment workload is heavy, modeling speed is slow.This paper describes two kinds modeling methods and procedures by the engineering example.

Keyword：complex terrain;surface fitting;numerical modeling;bicubic spline interpolation;