A new semi-fragile digital image watermarking method based on genetic algorithm was proposed. This method requires the watermark robust to common operations such as JPEG compression, and be fragile to other malicious actions. The embedding strength of the watermark was determined adaptively based on the type of image local region and GA was used to optimize the location of the embedded watermark. Simulation results proved that the proposed method has no influence on the objective and subjective quality of the image and the watermark can embed large amount of information; more importantly, the method proposed can exactly accurately determine the location of the malicious attacks, which demonstrates its superiority over the other methods.