Skin deformation is an important problem in virtual human modeling, and two main goals are realistic and real-time deformation. First, the geometrical models of 3D human body and human skin are presented, and then a novel classification met hod is given. According to the method, the skin deformation is firstly classifie d into two classes named surface-model skin deformation and multi-layered-model skin deformation, and then the most popular surface-model skin deformation is di vided into four sub-classes, namely, rigid deformation, local deformation operat ors, SDD, and interpolation deformation. Each class is described in detail cover ing the merits and shortcomings. Finally, the problems of skin deformation and f uture directions are discussed.