In this paper, an efficient multi-focus image fusion approach is proposed based on scale vector norm of image nonsubsampled contourlet transform(NSCT). According to the analysis of multi-focus imaging mechanism, the defocused optical imaging system can be characterized as a Gaussian low pass filter. Combining with the NSCT of an image, whether a region is in focus or out of focus can be determined by its corresponding high frequency coefficients' energy. Therefore, a scale vector norm is put forward in this paper and the fusion principles for different sub-band coefficients are also presented based on the regional scale vector norm. Experimental results demonstrate the proposed method can extract more details from multi-focus source images at a large extend and achieve more satisfactory results compared with other NSCT based methods.