We present an automatic 3D hair modeling approach that makes use of geometric information from a given 3D virtual head model to obtain the initial envelope shape-points that cover the whole head using a series of geometric methods that simulate the hair growth process. Considering that natural hair has uneven thickness and irregular shape char5acteristics, we further refine the envelope shape-points and define the hair density and expansion with hair-clusters as the basic unit. The B-Spline function is then used to fit the curve cluster, finally obtaining the virtual hair 3D data by mapping the texture picture with transparency. The experimental results show that this method can obtain realistic 3-dimensional hair using very few manual operations.