Aiming at the problem of information extraction of suspected illegal buildings in cities, a new algorithm for extracting suspected illegal building information based on multi-scale segmentation method is proposed. Firstly, the remote sensing image is segmented by setting multi-scale segmentation parameters, then is preprocessed by orthorectification, radiometric calibration, and atmospheric correction. Finally, the influence of each parameter on the scale segmentation effect is analyzed through multi-scale segmentation experiment. The results show that when the segmentation scale is 150, the shape scale factor is 0.7, and the compactness scale factor is 0.3, the image segmentation effect is the best.