A wind speed detection system and a wind speed detection method are provided. The wind speed detection system includes a pipe body and a controller. The pipe body comprises a pressure sensing module and a suction pump. The pressure sensing module is connected to a first opening through a first pipe and connected to a second opening through a second pipe. The first pipe has a main pipe. Two ends of a first alternative pipe are connected to two ends of the main pipe. When the controller performs a self-checking operation, the main pipe is closed and the first alternative pipe is opened. The controller starts the suction pump to perform forward suction. The controller measures a first air pressure through the first pipe and measures a second air pressure through the second pipe by the pressure sensing module. The controller calculates a reference wind speed value according to the first and second air pressures.