A new image enhancement algorithm based on fractional differential was proposed to improve the lower visibility of traffic video images in bad weather or complicated situations. The characteristics of fractional differential operator (Tiansi) were researched and some points to be ignore in the existing fractional order differential template were applied to the new fractional order differential treatment to improve and update the fractional differential operator. The improved operator was compared with the Tiansi operator and 5 kinds of common image enhancement algorithms. The comparing results show that the proposed algorithm can enhance the details of an image with less noise. When a color image is processed, the improved Tiansi operator can maintain the image colors well , sharpen the grey level images with high frequency signals and do not increase the noise more. When a gray image is processed, the noise can be suppressed by increasing the pixel weight in the template center with much high frequency information. The different fuzzy traffic video images under various situations are tested. The testing results show that the studied algorithm is suitable for the vague traffic video images under bad weather, and the processing speed of the algorithm can meet the requirements of the real applications.