Aiming at the ineffective problem of traditional algorithm which traces, creates and fills the isoline with color. By improving the traditional grid tracing and area filling color algorithm, put forward the optimal tracing algorithm and area filling color algorithm based on boundary point. Through describing isoline data structure, and selecting isoline point, the optimal tracing algorithm is realized. The isoline area filling algorithm uses different method to fill the close area and linkage area. Realize algorithm model by using C++ program language in VC++6.0 integrated developing environment. Experiment results show that this method can effectively resolve isoline creation and filling problem. And the method is simple and easy to realize.