High-strength steel forgings for an automobile face the problem of quenching cracking in production, and it is urgent to trace the cause of cracking from the production process. Therefore, the high-strength steel forgings after quenching for an automobile were dissected, and the crack morphology, metal streamlines, microstructure and element distribution were observed. Then, it was found that the material flow at the fracture was extremely uneven, and the severe slip and shear during the forging deformation were the main causes of cracking. Furthermore, the quenching process of an automotive SAE5137H high-strength steel forgings for an automobile in PAG quenching liquid with the mass fraction of 9% (water-based quenching medium containing 9% polyalkylene glycol) was simulated, and it was found that the maximum equivalent stress at the location of quenching cracking was much lower than the tensile strength of material, the quenching stress is low. Comprehensive crack analysis test result and finite element analysis result show that the material flow is not uniform during the forging process of forgings, and severe slip occurs locally, which reduces the plasticity of material. Although there is no direct cracking after forging, the lack of plasticity under the action of quenching thermal stress leads to cracking. According to the reason of cracking, by reducing the local die fillet of pre-forging mold cavity at cracking position A  to R8 mm, and local heating at position B of the forgings, the quenching cracking ratio of the forgings is significantly reduced, and the cracking problem is solved.