It has been widely reported that the thermocapillary effects always strengthen the droplet migration velocity as long as the temperature increases along the direction of Poiseuille flow. The insoluble surfactant, on the other hand, always retards the droplet migration. This is due to the fact that, for most of the models, the Langmuir equation of state for the surface tension is usually simplified, and the thermo-induced and surfactant-induced Marangoni forces are therefore decoupled. In this talk, we will show a thermodynamically consistent phase-field model for investigating the coupling effects of temperature and surfactant concentration on droplet migration under a fully developed Poiseuille flow. By choosing the interface free energy sophisticatedly, the surface tension of our model consists of not only the classical linear part for the thermocapillary effects but also a nonlinear coupling term of temperature and surfactant concentration that recovers the Langmuir equation of state. Through 3D numerical simulations, we find that this nonlinear coupling term introduces extra thermo-induced and surfactant-induced Marangoni forces to the droplet migration, leading to a competition between the two, especially for the case of high surfactant concentration.