To make the image secure and encryption faster, this paper proposes a simple three-dimensional chaotic mapping based on the idea that the image’s pixels can insert the adjoining pixels and the thought of stretching and folding the image. First of all, the algorithm changes the two-dimensional decimal matrix into a three-dimensional binary matrix. Second, based on the thought that the image’s pixels can insert the adjoining pixels, that is left mapping or right mapping, and the thought of stretching and folding the image, it changes the three-dimensional binary matrix into two-dimensional binary matrix. Third, the compound chaotic algorithm is used to scramble the decimal matrix, and the folding algorithm is used to change the two-dimensional binary matrix into threedimensional binary matrix. At last, it changes the three-dimensional binary matrix into a two-dimensional decimal matrix, and the decimal matrix is the encryption image. Experiments show that the image encryption is rapid and highly secure, and it can change the value of pixels element.