The structure of image background clutters is irregular and complex,while the structure of the target is regular and simple.The structural differences between them provide an effective way for clutter modeling.This paper proposes a new method to characterize background clutters based on the images structural complexity.Firstly,the directional gradient histogram can effectively characterize the structural information of the image,and the entropy of directional gradient distribution in the local region of the image is used to characterize the structural complexity of the corresponding region.Secondly,considering that the visual system of human eyes is sensitive to the contrast of the image,the differences between background clutters and the target are measured in image direction gradient distribution entropy space and contrast space respectively,and the background clutter model is constructed by weighted summation of standard variance.Finally,the relationship between background clutters and target acquisition performance is deduced,and the target acquisition performance evaluation model of the photoelectric imaging system is established.The model is verified by using open datasets.The experimental results show that the target acquisition performance evaluated by the proposed method is consistent with the actual target acquisition performance in the field,and the proposed method is superior to the existing clutter modeling methods in terms of Root Mean Square Error (RMSE) and correlation.