Geometric expansion model is an intuitive tool to assist in teaching solid geometry. It consists of foldable and unfolded planar shapes and solid frames, covering the unfolding structures of common geometric shapes such as cubes, rectangular prisms, and cylinders. It can be unfolded into a planar network diagram with one click along the hinge, and then folded and restored. Students can use their own hands to "flatten fold" and intuitively understand the source of the surface area formula, allowing them to intuitively understand the correspondence between solid shapes and flat unfolded diagrams, transform solids into planes, help them master geometric features, understand the derivation of surface area formulas, and cultivate spatial transformation thinking.