The utility model provides a rail welding seam ultrasonic detection device includes main part (1), its characterized in that of, main part (1) horizontal one side sets up first cantilever (21), and first cantilever (21) end sets up first railhead probe (211), main part (1) opposite side sets up second cantilever (22), and second cantilever (22) end sets up first railhead probe (212). 3 pairs of probes of rail welding seam ultrasonic detection device configuration, have 6 kinds and sweep the mode of looking into, coordinate special inspection equipment, can one time volume form defect and plane defect in the short -term test welding seam, the detection efficiency height. The current craft of regulation is detected a flaw the calibration block and can't be satisfied the sensitive calibration needs of ultrasonic detection device completely in the standard.