Front-tracking method (FTM) is used to study droplet motion caused by Marangoni effect with a point heat source in the diagonal direction. Droplet motion at different Marangoni (Ma) numbers was simulated. It was found that the droplet velocity which decreases as Ma number increasing, increases rapidly to a stable migration velocity then decreases. However, it reverses at t=1.2, which increases as Ma number increasing. Whereupon, the vortex of Hill sphere split and the vortex center moved slightly. The same reflux exists in the droplet as in the Hill sphere vortex. With the increasing of Ma, end topology of temperature field bifurcates twice: The lowest temperature point jumps into the droplet from the stagnation point when occurs firstly in the lower critical Ma number; The inner shell cooling zone breaks from the central point when occurs secondly at upper, then forming toroidal cooling zone.