The invention provides a carburizing and quenching method for a large heavy-duty gear; the method includes a segmented temperature-rising temperature-equalizing step, a carbon potential gradual-reduction carburization step, a segmented temperature-lowering temperature-equalizing step, a stepped quenching step, and a low-temperature tempering step. The carburizing and quenching method for the large heavy-duty gear not only can shorten the heat treatment period, improve production efficiency and save energy consumption, but also can effectively control heat treatment deformation of the gear, optimize a metallographic structure of the gear surface and improve comprehensive mechanical properties of the gear.