To solve the stability problem of multi-infeed direct current（MIDC） transmission system， a new type double-infeed direct current（DIDC） system is introduced， which consists of a high voltage direct current（HVDC） subsystem and a voltage source converter-based HVDC（VSC-HVDC） subsystem. Based on dq synchronous rotating coordinate， an independent decoupling control strategy for active power and reactive power in VSC-HVDC system is proposed. And the coordinated control of DIDC is implemented. With capability of fast reactive power regulation in the VSC-HVDC system， stable operation of DIDC system can be achieved by coordinating conventional reactive power compensation devices into VSC-HVDC system. Experiments on PSCAD/EMTDC simulation platform show that， under disturbance circumstance， the DIDC system control can not only effectively maintain the stability of bus voltage at inverter side， but also prevent reactive power compensation devices from frequent switching and reduce the commutation failure risk， which is in favor of improvement of operation reliability of the system.