As an important area of computer graphics, realistic image synthesis provides principles and techniques for creating realistic imagery through computations based upon models of real-world objects and behaviors. Facial expression is one of the primary communication means of the human. The ultimate goal of realistic image synthesis is to achieve perfect realism -the synthesized images are visually indistinguishable from their real-world counterparts. This area has widespread applications in industry and scientific research including 3D design, omputer animation, scientific visualization and virtual reality Facial expression synthesis has many useful applications in practice. How to synthesize facial expression images robustly and simply is still a challenging problem. This paper surveys the state of the art in this area.