In order to improve the performance of the acousto-optic frequency shifter, the positional mismatch characteristics between the internal acousto-optic crystal (AOC) and piezoelectric ultrasonic transducer (PZT) electrodes are studied, and several geometric assembly mismatches between AOC and PZT electrodes are analyzed. By constructing a three-dimensional finite element model of AOC and electrode mismatch, the ultrasonic sound field in the AOC is simulated and analyzed under different axial assembly dislocation conditions. According to the acoustic field distribution characteristics of ultrasound, it can be found that the geometrical assembly dislocation will lead to the formation of an area without acousto-optic interaction inside the AOC, and the relationship between the length of this area and the amount of dislocation can be revealed. By analyzing the optical interface between the acousto-optic interaction area and the non-acousto-optic interaction area, it is found that the position mismatch will cause the double-beam interference effect in the output light, which will affect the output of the actual optical system. Based on the principle of double-beam interference, an experimental system is built to measure the length of without acoustic interaction occurs region, and the results prove the rationality of the theoretical analysis.