The invention relates to a lightweight method applied to urban three-dimensional model data, and the method comprises the steps: S1, enabling an obtaining module to obtain a target image, and enabling a drawing module to draw a scene model according to the target image; s2, dividing each scene model into a plurality of layers by a division module, and storing the layers in a database module; s3, the matching module calculates the actual resolution A according to user requirements to select the corresponding scene model, and the scene model is displayed through the display module; s4, the statistical module calculates the actual display score B of each scene model so as to select whether to delete the corresponding scene model, the urban model data can be accurately updated and replaced, so that the size of the urban model data can be effectively reduced, the lightweight of the urban model data is completed, and the user experience is improved. And thus, the data lightweight efficiency is ensured.