Considering that material parameters of U-shaped electrothermal actuators are affected by the temperature nonlinearity and the discontinuous boundary problem in the simplified model, the transient displacement characteristics were studied. By introducing temperature-related material renewal functions, based on thermodynamic theories such as energy conservation equations and material mechanics theories such as virtual work principles, the electro-thermal-mechanical coupling model of U-shaped electrothermal actuators was established. The improved Chebyshev spectrum method was used to solve the constructed coupling model, and the expression of temperature and transient displacement of U-shaped electrothermal actuator was obtained. The results of finite element simulation and theoretical analysis were basically the same, verifying the correctness of the model. An experimental platform for the transient displacement characteristics of the electrothermal driver was built, and the displacement response experimental results of the U-shaped electrothermal driver under constant voltage excitation were compared with the theoretical and simulation results. The transient displacement characteristics of the driver under the action of a periodic sinusoidal voltage were analyzed. The test and analysis results show that the displacement change trend of the U-shaped micro-electric thermal driver showed a sinusoidal change after a period of time, and the change period was equal to the voltage period; the displacement change range varied positively with the peak-to-peak voltage, and negatively with the change in voltage frequency.