Abstract: A novel image encryption algorithm is presented.The algorithm uses the improved general Arnold map scramble image pixels in the spatial-domain.Then the sequence values of an improved Lorenz chaotic system is adopted to generate keys for the second grayscale image encryption.The key space is large enough to avoid the deciphering by the phase-space reconstruction theory and exhaustive method.The experiment demonstrates the algorithm is effective in the image encryption.The ciphered image has random-like distribution behavior of grey values，adjacent pixels have zero co-correlation properties and the deciphered image is perfect.