Abstract: In order to solve the rapid increase of the encryption time because of the increasing image size in the existing image encryption algorithm, the optimized encryption algorithm based on logistic and Arnold mapping was used to achieve the optimization of the fast image encryption algorithm. The algorithm was based on two kinds of chaotic maps to the original image, pixel scrambling and gray value substitution. Pixel scrambling was to select the H adjacent pixels according to the image size, appropriately adjust the H value and realize the encryption time optimization. Gray value substitution is to generate chaotic sequences by Arnold mapping, operate the scrambling image and get the cipher image. The results show that, for 256×256 Lena standard images, the encryption time is reduced to 0.0817s. The algorithm has advantages of large key space and fast encryption speed, and can effectively resist the attack of exhaustive, statistical, and differential means.