To address the learning difficulties faced by undergraduate students with weak mathematical and physical foundations in the highly abstract and complex subject of Special Relativity, this paper proposes a teaching method for Lorentz transformations utilizing two-dimensional planar diagrams, based on the graphical method introduced by Brehme. Relying on the invariance of the spacetime interval derived from the principle of the constancy of the speed of light, this method employs Euclidean geometric constructions to establish 2D diagrams. Through the geometric relationships within these diagrams and elementary mathematical operations, key spacetime relationships in Special Relativity—such as the relativity of simultaneity, length contraction, time dilation, and the Lorentz transformations—can be deduced. This pedagogical method requires only elementary mathematical knowledge, avoiding the need to delve into the profound physical concepts and complex mathematical derivations underlying Special Relativity. Its intuitive presentation makes it easy for beginners to master.