Abstract: It's very active in the research of CAD to construct smooth three boundary surface until now.Generating surface by PDE is a new method for surface modeling.In this paper,the smooth three boundary surface is generated using numerical method for solving partial differential equations(PDE).The author derives the difference form for PDE on generating GC⁰ or GC¹ three boundary surface using numerical integral method and gives the algorithm.The method for surface modeling constructs complicated surface satisfying the complicated constraint condition and can be applied to filling the hole of surfaces etc.