The advantages of Shape Memory Alloy (SMA) springs include small volume, straightforward construction, strong driving force, and excellent work-mass ratio. In this study, we propose a small temperature-controlled SMA linear actuator. A bias linear actuator is created by combining the driving element—the SMA spring—with the return spring. The linear actuator's mechanical design and fundamental operating principle are explained. The actuator's transient temperature field simulation is performed using the finite element approach. The temperature field of the actuator and the time required for complete phase transition of the SMA spring are studied. Proportional-Integral (PI) temperature controller is designed. The linear motion experiment is carried out for the linear actuator prototype. The experimental results indicate that the SMA linear actuator has a large linear motion range, meeting the design index of 12 mm running stroke. The displacement-temperature mapping model is nonlinearly fitted based on the experimental data. The model's correctness and error range are also confirmed through experiments.