A quantum dot (QD) composite material includes at least three QD structural units arranged sequentially along a radial direction. Among the at least three QD structural units, each QD structural unit at a center of the QD composite material and each QD structural unit at a surface of the QD composite material have a gradient alloy composition structure with an energy level width increasing along the radial direction from the center to the surface, along the radial direction, energy levels of adjacent gradient alloy composition structures of the QD structure units are continuous. A QD structural unit located between the QD structural units at the center and the QD structural units at the surface have a homogeneous alloy composition structure.