In this paper, an RGB color image encryption method based on the Lorenz chaotic system and DNA computation is presented. This method can not only change the location of the image pixel but also change the pixel values. Firstly, we split the RGB color image into R, G, B three components. Then, we use the 2D-hyperchaotic sequence to disorder the location of R, G, B three-component pixels. Secondly, three different chaotic sequences are generated by a one-dimensional logistic chaotic map, and the pixel values of the three components R, G, B can be scrambled through the three logistic chaotic sequences. Then the R, G, B digital images can be transformed into DNA coding matrices based on DNA coding rules. Thirdly, 3D chaotic sequences are generated by use of Lorenz chaotic system and are encoded based on DNA encoding rules in order to generate three DNA sequences. Finally, the encrypted image can be obtained by utilizing DNA operations on the DNA sequences of three components R, G, B and DNA sequences generated by the Lorenz chaotic system. The experiment results and encryption effect demonstrate that the proposed scheme is effective, and it has strong sensibility, high security, and good ability of resisting statistic attack.