Structural members and kinematic pairs made of rigid materials can be flexibly used in practical applications and obtain shape-changing mechanisms. However, it also leads to a relatively complex mechanical structure and overmuch kinematic pairs, which increases the difficulty of controlling the mechanism and thus limits its application. The emergence of 4D printing technology and smart materials provides new ideas for simplifying shape-changing mechanism structure and innovation. Although smart materials are already being used in many types of mechanisms, they are almost always unique cases. How to organically combine with a specific mechanism, innovate the type of mechanism, and systematically research from structural design to deformation control is still a blank area. Therefore, this paper designs a type of novel mechanism consisting of an angulated scissor unit and a form-controlled unit, the form-controlled planar scaling mechanism, which can achieve drivable self-adjustment of size ratio under predetermined thermal stimulation. The shape-changing mechanism is thus extended to a form-controlled mechanism. This mechanism's construction method and structural principles are analyzed, and the critical structural design parameters required for deformation control are derived. Based on the above research, the core form-controlled unit that controls the deformation of this type of mechanism is designed structurally and extended to deformation control research. Finally, two sets of prototype machines are manufactured and verified the feasibility of the construction method and deformation control scheme and the correctness of the theoretical analysis. This type of mechanism promotes the innovation of mechanism design methods. It shows many application prospects in satellite deployment structures and space probe walking systems.