The invention proposes a bit-level image encryption method based on composite Tent chaotic mapping, and the method comprises the steps: firstly, carrying out the coupling of Tent mapping, Logistic mapping and Sine mapping, obtaining a composite chaotic mapping TLS, improving the complexity of a chaotic system, enhancing the randomness of a secret key sequence, enabling the parameter range of the chaotic system to be expanded, and achieving the encryption of a bit-level image. Therefore, the security of the encryption system is effectively improved. And compared with a high-dimensional chaotic system, the execution cost of the one-dimensional chaotic system is lower. A plurality of composite chaotic systems are introduced in the encryption process to increase the number of keys, the key space of the algorithm is expanded, and the algorithm can well resist violent attacks. A matrix splicing method is used in the scrambling process, and the problem of bit limitation during bit scrambling is solved. Two rounds of XOR operation are used in the diffusion process, and the differential attack resistance of the encryption system is effectively improved.