A model-adaptive multi-source large-scale mask projection 3D printing system configured to conduct the following steps: projecting pure-color images of first and second colors having identical attributes, capturing an image of an overlapping portion and calculating height and width information of the overlapping portion; splitting a pre-processed slice and respectively recording width and height information of two slices resulting from the splitting and generating two gray scale images having identical attributes thereto; counting power values of identical positions of slices in different gray scale values, performing a further calculation to obtain a projection mapping function, using the projection mapping function as a basis for performing optimization on gray scale interpolation of the generated images; and fusing the processed gray scale images and the originally split two slices to obtain a mask projection 3D printing slice having a uniform shaping brightness, and forming a final product.