In this paper,by combining the information entropy with the image blocking,an evaluation method of image scrambling degree based on block information entropy variance is proposed.The basic principle of the evaluation method is elaborated,and some simulation experiments are carried out to evaluate and analyze the degrees of the pixe llocation scrambling based on the Arnold transformation,the pixel gray value scrambling based on the Logistic chaotic mapping and the Arnold-Logistic cascaded pixel location and grays crambling,respectively.The results show that the proposed method is correct and effective in evaluating the image scrambling degree.Moreover,further experiments on different images encrypted by the same algorithm show that the proposed method is suitable for the security evaluation of encryption algorithms because it helps to obtain evaluation results independent of primary images,and that the method is simple in principle,easy in realization and convenient in usage due to the non-engagement of primary images in the evaluation process.