The traditional image encryption with scrambling-diffusion structure is usually divided into two independent steps of scrambling and diffusion， which are easy to be cracked separately， and the encryption process has weak nonlinearity， resulting in poor security of the algorithm. Therefore， a scrambling diffusion synchronous image encryption algorithm with strong nonlinearity was proposed. Firstly， a new sine-cos chaotic mapping was constructed to broaden the range of control parameters and improve the randomness of sequence distribution. Then， the exclusive-OR sum of plaintext pixels and chaotic sequence was used as the initial chaotic value to generate chaotic sequence， and this chaotic sequence was used to construct the network structures of different pixels of different plaintexts. At the same time， the diffusion value was used to dynamically update the network value to make the network dynamic. Finally， the single pixel serial scrambling-diffusion was used to generate cross-effect between scrambling and diffusion，and the overall synchronization of scrambling and diffusion， so as to effectively resist separation attacks. In addition， the pixel operations were transferred according to the network structure， which made the serial path nonlinear and unpredictable， thereby ensuring the nonlinearity and security of the algorithm. And the adjacent node pixels sum was used to perform dynamic diffusion in order to improve the correlation of the plaintext. Experimental results show that the proposed algorithm has high encryption security， strong plaintext sensitivity， and is particularly effective in anti-statistical attack， anti-differential attack and anti-plaintext attack.