Fatigue failure of gears carrying heavy loads is the leading cause of gearbox breakdown in the large-scale earthmoving machinery. The fatigue life of gear is mainly determined by loads distribution. Taking the Wheel Loader as an example, this paper introduced an indirect test system of gear load under the loose soil conditions. Then the load data in time, amplitude and frequency field were respectively analyzed. The results show that the indirect measurement method proved workable, and the load data of gear is characterized by bi-modal. Therefore, to decrease statistical errors, mixture model must be adopted to fit these bi-modal signals.