The present invention relates to a 3D printer with an exposure system for a large-scale screen. The 3D printer of the present invention comprises a resin tank configured to be filled with liquid resin; a build platform configured to be immersed in the resin tank or positioned on a surface of the resin tank to form a building plane, and make the liquid resin be cured and stacked on the building plane; a build-platform driver configured to drive the build platform to move up and down; an exposure system configured to project an image beam toward the building plane; and a controller configured to generate a layered unit image from shape information about a building object, split the layered unit image into a plurality of split images, and provides the plurality of split images to the exposure system with time differences, wherein the exposure system receives the plurality of split images from the controller and projects a plurality of split image beams with time differences, and the plurality of split image beams is made into the image beam by a plurality of split screens with time differences and projected to the building plane. The present invention provides a 3D printer which employs one optical engine to form a large-scale screen, thereby having a simpler structure and costing less than a system using a plurality of optical engines.