The present disclosure provides a backlight source flatness detection system and a backlight source flatness detection method. The backlight source flatness detection system includes: a working table, a support column, a detection device, a processor and a display device. The working table is transparent and carries a to-be-detected backlight source. The support column supports the working table. The detection device is below the working table and detects distances between the detection device and at least two detection positions of the to-be-detected backlight source. The at least two detection positions includes at least one position of a center area and at least one position of a peripheral area. The processor is connected to the detection device and processes a detection result from the detection device so as to acquire a warpage value. The display device is connected to the processor and to display the warpage value acquired by the processor.