Abstract: So far most of the papers ignore the MMC module when building the small signal model of the transmission system, the loss of which actually has impact on the transient characteristics of the system through affecting the DC-side active power output of converters. First, the average value model was applied to the small signal model of MMC after being transformed into two-phase synchronous rotating coordinate system. This can well reflect transient response of MMC’s external characteristics to the connected DC and AC Networks as well as takes the loss of MMC into account. Second, considering the small disturbance response between the phase angle at common coupling point and the equivalent impedance of AC network, small signal model of phase-locked loop was improved. Final, the small signal model of the whole HVDC transmission network was built, and its accuracy and effectiveness was verified by the comparison with the simulation results of electromagnetic transient model in PSCAD.