In this paper, a high-voltage direct current (HVDC) tie-line has been accurately modeled and proposed for multi-area interconnected power system to enhance load frequency control and automatic generation control (AGC). HVDC tie-line has been modeled based on a simple first-order transfer function for AGC system. Time constant of this transfer function indicates the required time by HVDC to set DC current because of load perturbation in multi-area interconnected power systems. It is worth mentioning that the inexact and very simple model of HVDC-line cannot yield a reliable and correct response. Hence, an accurate and interpretable model is proposed for HVDC-link to control the AGC system. To verify the accuracy of the proposed model, it has been analytically compared with the conventional HVDC model. The integrated multi-area power system has also implemented the inertia emulation controller technique which enables AGC system to tackle the accumulated energy in HVDC-line’s capacitance.