Face recognition technology is advanced, but its recognition rate is also 100% accurate. There are also some difficult problems that are difficult to overcome, such as human expression and illumination, which will affect face recognition. Here is a brief introduction. First, illumination change is the most key factor affecting the accuracy of face recognition. Because the face is a 3D structure, Therefore, the shadow cast by ray will strengthen or weaken the characteristics of the original face. Especially at night, the face shadow caused by insufficient light will lead to a sharp decline in recognition rate, which makes the system difficult to meet the actual requirements. At the same time, theory and experiment also prove that the difference between the same individual under different light is greater than that between different individuals under the same light. 2ã Facial expression change facial expression change is composed of different expression expression areas, including mouth, cheek, eyes, eyebrows and forehead. Human emotional expression is realized through local deformation of the muscles that make up the expression area. These changes are not simple translational and rotational rigid changes. The local deformation of facial muscles caused by expression changes will be regarded as a part of facial feature patterns, so it is difficult to distinguish whether the differences between feature patterns are caused by different faces or expression changes, which makes classification and recognition difficult.