In order to make the aiming line aim at the target and make the image stable, the 1:2 transmission mechanism is used in the periscope upper reverse mirror system. The existing 1:2 transmission mechanisms are investigated and the advantages and disadvantages of these mechanisms are analyzed. On the basis of the existing structure, a new type of 1:2 transmission mechanism is designed. The designed new type of transmission mechanism is a rolling bearing three connecting rod mechanism, which is connected by the bearing between the swing rod and the rotor, and the sliding connection is transformed into a rolling connection. The friction torque is reduced as much as possible so as to achieve a better image stabilization effect. The experiment shows that the 1:2 transmission mechanism has simple structure, good reliability, good transmission stability, high precision and without the influence of temperature. It can achieve good transmission and stable accuracy.