Disclosed is a thermosetting composite resin composition including a thermosetting resin, particularly an unsaturated polyester resin, a low-profile additive and an inorganic filler, and to a method of manufacturing an automobile shell plate using the same. The thermosetting composite resin composition can be used to manufacture not only automobile shell plates having low specific gravity and superior surface smoothness and mechanical properties but also structural parts such as interior parts for airplanes or railways.