A new method was presented to retrieve medical image, which is based on mutual information method. A database of ultrasonic images was retrieved by the method. The result shows that this method not only has the features of translation invarant, rotation invariant and scale invariant, but also avoids image segmentation which may lead to a complex calculation. The method has the advantage that the speed of retrieval will not get slow with the increase of the number of images. This new method can also be used to retrieve similar non medical image.