Abstract: 700L steel trailer frame beam products in an enterprise under lower service lives cracked. The reason for cracking of the beam was analyzed by testing the fracture morphology, chemical composition, microstructure, mechanical properties, fatigue performance and service performance of the cracked beam, and comparing with those of the uncracked beam. The corresponding improvement was put forward. The results show that the structure of the cracked 700L steel trailer frame beam had mixed crystal phenomenon, led to low toughness and fatigue limit. Under the alternating load, stress concentration occurred at the position between the spring support and the reinforcing plate on the lower wing surface of the beam and the connection between the saddle plate and the beam. Microcracks initiated and growth at the stress concentration position, and eventually led to fatigue fracture of the frame beam. To reduce the risk of cracking, the final rolling temperature should be lowered slightly, and C-shaped reinforcing plate was placed near the inner side of the lower wing surface of the gooseneck to decrease stress concentration of the beam under service conditions.