Sensing unit (or photoelectric effect unit) of optical voltage transformer is the key part of the transformer, which has an important effect on the structure and performance of the transformer. Basic principle of a kind of reflective optical voltage transformer was introduced in the paper. The voltage sensing unit based on Pockels effect was designed and produced. Three insulating and shielding devices for experiments simulating power system high voltage insulating and shielding device were designed. Experimental study was made for sensing unit using the optical voltage transformer system. The test results under 0~2.5 kV direct voltage at room temperature showed that the output of the transformer had a good linear relationship with the three insulating and shielding devices respectively, indicating the feasibility of the sensing unit.