The intrinsic linear birefringence and its temperature characteristic of the BGO crystal seriously restricts the development of optical voltage sensor, thus the study on the intrinsic linear birefringence is of great significance to improve the performance of the optical sensors. An interference fringes method employing a crystal wedge was proposed in this paper, and the measurement for the intrinsic linear birefringence of the crystal inside the sensing head can be realized by measuring the fringes′ displacement. The theoretical deduction of the measuring principle was given taking Jones matrix as a mathematical tool, the application example and the verifying results were also given, which indicates that the intrinsic linear birefringence and its temperature characteristic can introduce an error of about 1% to the voltage sensor. Compared with the traditional intensity method, the measured results of this method are insensitive to the power fluctuation of light source, and there is no adjustment of any optical components during the whole experiment, so no additional error will be induced. The measurement accuracy is improved by about one order of magnitude.