The invention discloses a compact optical retarder which comprises a casing. A double fiber collimator is connected with one end of the casing. Inside the casing, a cat eye reflector is arranged at a position close to the tail. A gap is arranged between the cat eye reflector and the double fiber collimator. A roof prisms are arranged inside the casing. The roof prisms are distributed in an input-output optical path between the cat eye reflector and the double fiber collimator. A motor is arranged on the other end of the casing. A clamp is connected between the motor and the cat eye reflector. According to the compact optical retarder, by arranging the cat eye reflector, the entire retarder is more compact; the size of the compact optical retarder is much smaller than the size of a traditional adjustable retarder; the motor and the cat eye reflector are connected through the clamp, which facilitates the reflection position adjustment of the cat eye reflector; and the design rationality is ensured.