A new approach of degrading image is presented. This method has four steps: obtain the number of the subimages first, and then these subimages are constructed, the third step is calculating the weight of each subimage according to its velocity, at last motion-blurred image is constructed by weighted accumulating the subimages. We compared the effects between the method of this article and existing algorithms by using accelerated motion-blurred images and retrace motion-blurred images separately. The maximum absolute differences between the accelerated motion-blurred images degraded by the method of this article and the existing algorithms which are discrete convolution (DC) and discrete Fourier transform (DFT) are 2.5580×10<sup>-13</sup> and 3.4106×10<sup>-13</sup> separately. And the maximum absolute differences are 2.5580×10<sup>-13</sup> and 3.4106×10<sup>-13</sup> separately for retrace motion-blurred images. It can be proved that the performances of different methods are the same. The time consumed by degrading images of different forms of motion is less than half a second, close to the time consumed by DFT, but hundreds of seconds shorter than DC. What’s more, the process of the method of this article strongly resembles the real imaging process, so it can be comprehended more easily than the existing algorithms.