The temperature stability of the optical fiber voltage transformer (OVT) has always been the key factor restricting its practical application. There are many factors affecting temperature characteristics, including residual birefringence during Bi4Ge3O12 (BGO) processing, the thermo-optic effect, the thermal expansion effect, and temperature change of the second-order nonlinear polarization coefficient. These complex effects interact with each other and affect the temperature characteristics of the OVT. Therefore, for a long time, the research of various literatures has not been comprehensive enough, and even has certain contradictions. In this paper, the mechanism between the five influencing factors and the OVT temperature characteristics was investigated. The experimental results show that the temperature characteristics of OVT can be divided into two aspects: the starting point and the conversion coefficient. The starting point is affected by the residual birefringence of the BGO crystal, crystal alignment, the thermal expansion of the crystal, and the thermo-optic effect. The conversion coefficient is affected by the starting point, the thermo-optic effect and the second-order nonlinear polarization coefficient.