Abstract: Internet is a double-edged technology,it pushes the development of multimedia,yet many pornographic images and videos might make problem to young generation.Techniques are needed to keep these images away from children.We developed a hierarchical nude image detection system.In the processing,images are first filtered by skin color model.Then,images are classified by support vector machine.Finally,images are verified by nearest neighbor.Experiments show that 85% images contain nude could be filtered accurately.