Quantum image encryption is a hot research topic in recent years. In this paper, a novel quantum image encryption algorithm based on quantum key image is presented, which has low complexity than other algorithms. The quantum key image is a special quantum image which is used to store the encryption keys. The encryption keys are generated by a cryptographic algorithm, and are prepared into the gray value of the quantum key image. Based on this quantum key image, the plain image does the XOR operations with it bit by bit. The circuit of the encryption algorthm is given, and the numerical simulations and theoretical analyses are done. The proposed encryption quantum image algorithm is efficiency, and it has large key space and lower computational complexity.