Aiming at the droplet transfer behavior under actions of laser plasma and arc plasma together, the origin and action principle produced the force on droplet are profoundly analyzed according to the theory of gas dynamics and the static force balance. The experimental results indicate that the rejecting force caused by metal vapour prevents the droplet from detaching when the material evaporates at the high power density of laser. On the other hand, the laser plasma from laser-induced keyhole changes the original path of MIG arc plasma, which results in that the current density distribution and flow of conventional MIG arc are varied, and produces a new hybrid electromagnetic force in the CO2 laser-MIG hybrid welding process. As a result, the droplet transfer frequency is decreased, and the welding process becomes unstable. Furthermore, the influence of welding parameters on vaporization-induced recoil force and the hybrid electromagnetic force caused by laser plasma and arc plasma together are also studied, and the mathematical descriptions is deduced by adopting numerical analysis, which consequently analyzes the force mechanism of droplet quantitatively, and discloses the internal relationship between the force state of droplet and welding stability in CO2 laser-MIG hybrid welding process.