It becomes necessary to utilize electromagnetic/ electromechanical hybrid simulator to modern large HVAC and DC power system, where multiple HVDC links feed into concentrated load areas. In this paper, a practical real-time hybrid simulator is proposed. The simulator makes RTDS and external transient program running on a computer link together effectively and smoothly. The entire interface schemes for hybrid simulation are discussed on both algorithm and implementation layers. Aiming at the problem on unexpected low frequency non-characteristic harmonics, an impedance angle preserved circuit is employed, with fast parameter calculation method. At last, based on a large case system of China Southern Grid, the hybrid simulator is compared to the electromagnetic simulation on 27 RTDS racks to validate and verify the proposed scheme.