Shadow removal plays an important role in the moving object detection and retrieval of surveillance system. In order to remove shadow effectively, a detailed data analysis about shadow attribute is given after a brief introduction about how shadow comes into being. It is concluded that compared with the same field in background, the luminance of the shadow decreased a little, while each chroma per centum does not change a lot in RGB model. However, each chroma per centum of the moving object does change a lot. According to it, the paper proposes an easy algorithm which first picks up the front moving object, and detects the shadow in good use of the different properties between the shadow and object, and finally removes it successfully. The experiment shows that the algorithm could indeed remove the shadow coming from moving object effectively.