Edge detection is always study focus in the field of medical image processing and analysis. It is an absolutely necessary step in medical image processing. In China medical field, processing of real-time data is constrained by limited resources .Thus, it is important to understand and analysis image analysis algorithms for accuracy, speed and quality. In this paper are analyzed the frequency features of the （Sobel,   Prewitt ,  Robert , Laplacian, Canny operators） from the viewpoint of frequency and speed domain, and it is proposed that the frequency features of the different operators should be considered when different operators are being used or constructed. Because edge detection operators is sensitive to the edge type, the appropriate operator should be adopted should be adopted in different edge type detection. Finally, the importance and necessary of comparing the continuity and speed edge detection operators are validated in the area of MRI image.