Abstract: The measurement accuracy of the reflective fiber optic voltage sensor (RFOVS) is greatly affected by the change of physical parameters of quartz crystals under the temperature disturbance. In this paper, a mathematical model of system thermally induced error of the RFOVS was established by using Jones matrix. Combined with the finite element method, the influence of the change of quartz crystal physical parameters (circumference, height, piezoelectric coefficient) under the temperature disturbance on the output accuracy of the system was investigated based on the proposed model. The research results show that the change of crystal circumference has the most serious impact on the output accuracy of the system, followed by the piezoelectric coefficient, and they all can not meet the requirements of IEC 0.2S accuracy level in the temperature range of -40℃~+85℃. However, the influence of height changes on system error is small, which keeps well within ±0.06%. In addition, the temperature variation has a linear relationship with the system phase error. This paper lays a theoretical basis for the thermally induced error suppression of fiber optic voltage sensors and provides some reference for system temperature compensation.