The invention discloses a photoelectric type derrick deflection detection device and a detection method thereof. The device comprises a laser emitter, a laser receiver, optical choppers, inclination sensors and a deflection detector, wherein the laser receiver and an inclination sensor are arranged at the upper end of a derrick, the laser emitter and an inclination sensor are arranged at the lower end of the derrick, and optical choppers and inclination sensors are arranged on all detection points of the middle of the derrick. When end portions of the derrick are subjected to a load action, the whole deflection of the derrick can be detected. According to the photoelectric type derrick deflection detection device and the detection method thereof, the device can detect the whole deflection value and a destabilization state after force is exerted on the derrick, bases are provided for the force analysis of the derrick, the optimization design of the derrick and the quality detection of the derrick, the precision is high, the range is wide, the accuracy is good, the structure is simple, the operation is simple, the producing cost is low and the data can be displayed in real time.