Abstract: A new segmentation method of the level set model based on prior information was proposed in this paper and was applied to crop diseased leaves with complex background. Firstly, structure tensor information was used to improve the LBF model, so that a new level set model was constructed with structure tensor information. At he same time, target shape was represent by the level set method. Secondly, prior shape information in the form of energy function was introduced to the new level set model and got the new level set model based on prior information. Finally, cucumber disease leaf images with complex background were segmented by the model. Experimental results show that the method can accurately extract the disease leaf from cucumber disease leaf images with complex background, which can provide the foundation for extracting, identifying and diagnosing the diseased spots.