Abstract： A fault reconstruction method based on terminal sliding mode observer was proposed in this paper. In the traditional sliding mode observer, the estimated error of unmeasured state is asymptotic convergence, which affects the timeliness of thruster fault reconstruction. In response to the above problem, the property of finite time convergence of terminal sliding mode was used to build a terminal sliding mode observer to ensure that all of the state estimation errors converge in a finite time. Then the thruster fault was reconstructed by using the equivalent output error infection method. Finally, the proposed method was validated by simulation.