The invention discloses a two-dimensional size adjustable plastic frame for a building template and an application method for the plastic frame. The plastic frame has a rectangular frame structure formed by combining two L-shaped high-impact-resistant plastic components, and the inner side of the rectangular frame structure is provided with a groove adapted to the edge of a template panel; the L-shaped plastic components are in 90-degree double-tenon connection, tenons and grooves on end parts of the two plastic components are riveted fixedly through vertically through rivets, and the size can be flexibly adjusted during application. The plastic frame is formed by hot working of high-impact-resistant plastics serving as a main material, the damage of a plastic template caused by falling, collision and the like in the using process can be effectively relieved, the plastic template is protected, the template is convenient to move to improve project progress, and the construction cost is reduced; the plastic frame can be cut according to the size of the template, is wide in application range and can be produced on a large scale; the plastic frame has high elasticity and can avoid leakage of a common template in the using process. In addition, the plastic frame is made of the high-impact-resistant plastics serving as the main material, can be recycled and belongs to an environment-friendly product.