Optical Fiber Voltage Sensor (OVS) has potential applications in power supply network, but upon to now the OVS can not be industrially used in practice. This paper introduces some problems we met in development of practical bulk-modulation OVS using BGO crystal. The optical source must be pre-modulated so that to detected the average optical power easily. The measure error, nonlinear distortion, sensitivity produced by deviation of optical element are discussed. Analysis and test show, that a small collimating error of optical elements will lead to decrease the sensitivity and increase phase shift. So long as the angle (alpha) between the polarizer and (lambda) /4 wave plate is equal to (pi) /4, the location of the polarizer for detection and BGO is not very important and the maximum sensitivity can be achieved when the angle (gamma) between the detected polarizer and BGO is equal to (pi) /4. But if (alpha) does not equal (pi) /4 and (gamma) does not equal (pi) /4, not only the sensitivity will be decreased, but also the distortion will be increased, depending on the angle (beta) between BGO and (lambda) /4 wave plate. So we use a quartz plate to hold (lambda) /4 wave plate. So we use a quartz plate to hold (lambda) /4 wave plate in order to obtain good circular polarization light. In order to eliminate the effect of random fluctuation of average optical power, some data process must be needed. We use 80C196KC single chip CPU to calculate the instantaneous value, and the effective value of measured voltage can be displayed in this transducer. We use silicon gel insulator to introduce high voltage to sensor. Some calculation and test results are given in this paper.