To address the demand for micro-actuators with large displacement and large driving force in the safety and arming device of Micro-Electro-Mechanical Systems (MEMS) fuzes, combined with the characteristics of Shape Memory Alloy (SMA) such as large strain and high energy density, research on SMA micro-actuators for fuzes was carried out. Considering the problems of low utilization rate of shape memory effect and obvious stress concentration in conventional SMA micro-actuators with uniform cross-section, the design and performance research of SMA micro-actuators with variable cross-section were conducted. The variable cross-section design was based on the stress phase transformation principle of SMA, and the cross-section size was adjusted according to the bending moment distribution on the beam to improve the stress distribution and phase transformation degree. COMSOL was used to carry out finite element simulation analysis on the driving performance of the SMA micro-actuator, a test platform for driving force and steady-state temperature was built, and tests on driving displacement under different tensile amplitudes and multiple cyclic tensile conditions, as well as tests on driving force under different temperatures were carried out. The results show that the maximum driving displacement of the variable cross-section micro-actuator reaches 2 mm, which is 66.67% higher than that before optimization, and there is no obvious displacement attenuation during cyclic use, with more uniform stress distribution; when stretched to 1.6 mm, the overall maximum stress decreases from 773 MPa to 542 MPa, a reduction of 29.88%; under the working condition of 250 ℃ and 1.6 mm displacement, the driving force is 11.28 N, which is 17.79% higher than that before optimization.