To better analyse the process parameters effects on distortion, a multi-field coupling simulation of the 42CrMo Navy C-ring vacuum oil quenching process is performed using DEFORM software. The cooling curves of different processes are measured using a stainless-steel probe, and the heat transfer coefficients are calculated by solving the inverse heat conduction problem to accurately predict the transient temperature field. The numerical analysis results demonstrate that increasing the oil temperature rarely affects the distortion. Decreasing the agitation frequency from 50 to 10 Hz can reduce the distortion by 48%. The pressure above the quenching tank has the most effect on distortion, as increasing the pressure from 10 to 50,000 Pa increases the gap by 1.5 times.