The existing fractal contact model fails to solve the problem of online real-time irregular curvilinear contact under mixed lubrication conditions. In this study, a novel arbitrary curve contact model is established, considering the actual operating condition that occurs under mixed lubrication. Furthermore, a new online friction–thermal–load coupling model for an arbitrary curve contact under mixed lubrication conditions is presented, considering the actual operating condition. To investigate the effects of the proposed online friction–thermal–load coupling model, a 30,205 tapered roller bearing with curved contact is examined by reading the real-time key point temperatures using thermocouple. Finally, the effectiveness of the presented model is verified through experiments and comparison.