The invention relates to a foundation pit barrier gate automatic control system and a control method thereof. The foundation pit barrier gate automatic control system comprises a PLC controller, a human body sensor, an open travel switch, a closed travel switch, an alarm device, a clamp proof sensor, a motor-drive circuit and a motor which controls the opening and closing of the barrier gate. The human body sensor, the open travel switch, the closed travel switch, the alarm device, the clamp proof sensor, the motor-drive circuit and the motor are connected with the PLC controller. The human body sensor is installed in a foundation pit. The open travel switch, the closed travel switch, the motor-drive circuit, the motor, the alarm device and the clamp proof sensor are installed on the barrier gate. The control method comprises the following steps: the human body sensor detects whether people exist in the foundation pit; the clamp proof sensor detects whether obstacles exist below the barrier gate in a falling process of the barrier gate; the open travel switch and the closed travel switch respectively detect whether the barrier gate reaches a highest point and a lowest point; and the opening and the closing of the barrier gate are automatically controlled according to whether the people exist in the foundation pit, so that phenomenon that automobile above the foundation pit is started when the people are working in the foundation pit are avoided; in addition, working safety factors are raised, and the personal safety of the working personnel in the foundation pit is ensured.