A blocking algorithm of digital color image encryption based on improved Logistic chaos sequence(NCA) is presented in this paper, the sub-block of R,G,B components are scrambled respectively. The new algorithm gets rid of restrictions on iterations of NCA. We use the significant figures of iteration value to be the matrix to replace the pixel value. The simulation results used by Matlab 7.0 show that the new algorithm has good advantages such as a larger key space, sensitive to initial conditions and better real-time characteristic, so it can protect the images security over the internet.