The invention discloses a metal bar flaw detection production line system and a method thereof. The system comprises a flaw detection system and a transmission device; the flaw detection system comprises a fixed support, a lifting device, a moving device, a flaw detection device and an adjustment device; the lifting device comprises a lifting cylinder and a supporting plate which slides up and down; the moving device comprises a third motor, multiple supporting rollers, a supporting device and a transmission component; the multiple supporting rollers are rotationally arranged on the supportingdevice in front-back distribution, one end of each supporting roller is connected with the transmission component, and the third motor is connected with the transmission component; a fixed block of the flaw detection device moves on a sliding rail along the length direction of a metal bar to perform flaw detection on the metal bar; and a rotating device comprises a transmission device and a pairof rotating roller sets arranged in bilateral symmetry inside a detection box, and a first motor drives the pair rotating roller sets on the transmission device to rotate. Through the metal bar flaw detection production line system and the method thereof, comprehensive flaw detection on the metal bar is realized, flaw detection on a single straight line or a peripheral face of the metal bar is avoided, and flaw detection efficiency is higher.