In view of the intrinsic difficulties of dim target detection and the shortcomings of common detection method,a new method of dim target detection based on scale slope feature of fractal surface was put forward. Compared with fractal features of fractal dimension and fractal fitting error,the scale slope feature of fractal surface is more obvious in representing the difference between target and background,and it is more robust than the traditional fractal features. This method is suitable for detecting dim targets in a natural environment,and it has higher detection probability especially for the small target in the sky. It is not affected by the target type,object pose,natural background etc. After fractal feature process,dim target can be detected through simple segmentation.