Considering the influence of heterogeneous characteristics on the demand side load resource regulation, a joint control strategy based on generalization index is proposed for heterogeneous thermostatically controlled loads (TCLs). The error correction and the behavior analysis is taken into account firstly, and the degree of refinement and applicability of the equivalent thermoelectric model for TCLs is further improved. Consequently, a generalization index is proposed with the consideration of the controllable energy space and the transferable time, which realizes the standard evaluation of the operating state of heterogeneous TCLs, and can be further utilized to guide the combinatorial optimization of heterogeneous load groups. Finally, the experimental simulation indicates that the proposed method can perfectly match the demand for the control of heterogeneous TCLs, and can maintain the control accuracy and improve the temperature distribution at the same time.