The invention provides an automatic detection method for a friction welding head of a conical component with a large length-diameter ratio. The automatic detection method comprises the following steps: a, placing the conical component; b, carrying out water immersion ultrasonic detection; and c, screening qualified parts. According to the invention, an automatic detection system is adopted for detection, and the automatic detection system comprises an equipment water tank, a guide rail assembly (10), a profiling positioning tool (20), a first push rod (30), a clamping, assembling and disassembling tool (40) and water immersion ultrasonic C scanning equipment. The profiling positioning tool (20) comprises a tool body (21), a second push rod (22), a sliding sleeve (23), a connecting rod (24), a first clamping jaw (25), a second clamping jaw (26) and a compression spring (260). According to the method, the flatness and the coaxiality of the conical component with the large length-diameter ratio on the ultrasonic C scanning water tank guide rail can be effectively ensured, so that the detection accuracy is ensured; and meanwhile, the method can realize rapid and automatic loading and unloading, saves labor productivity, is high in detection efficiency, and can realize large-scale detection.