The research progress of extrinsic doping of mercury cadmium telluride (Hg1-xCdxTe, MCT) materials in recent years is presented. The extrinsic doping of MCT refers to that an impurity doped is the element other than Hg, Cd or Te. The basic concept of a MCT crystal structure is described. The fundamental principles of MCT doping and the methods for selecting dopant are discussed, with an emphasis on the properties of some common dopant. In the design of a MCT detector, the control of the space distribution and concentration of a dopant is very important.