The invention discloses an image encryption and decryption method based on a fractional order translation chaotic system, and relates to the fields of computer cryptography, image encryption processing and communication and network engineering, which can solve the problems that initial conditions of an existing chaotic system are not associated with plaintexts, plaintext attacks cannot be resisted, and the safety is poor. According to themethod, translation transformation is conducted on the fractional order chaotic system by introducing a piecewise function, parameters are set, different numbers of scroll attractors can be generated, and the fractional order translation chaotic system perfects the field of fractional order chaotic systems composed of three-dimensional one-time autonomousconstant differential. Meanwhile, the fractional order multi-scroll chaotic system has higher dimension space and higher initial value sensitivity, the image encryption and decryption algorithm basedon the system is high in randomness and multiple in secret key parameters, a multi-iteration mode is adopted in the encryption process, an encrypted ciphertext matrix becomes very uniform, and therefore the purpose of effectively hiding original image information is achieved.