Abstract: The matching-control-based grid-forming permanent magnet synchronous generator (MC-PMSG) can improve the voltage stability of the sending-end power grid in the line-commutated-converter based high voltage direct current(LCC-HVDC) transmission system of wind power in desert and Gobi regions. However, when the MC-PMSG is situated in the vicinity of LCC-HVDC rectifier station, the SSO features are indeterminacy. Aiming at above-mentioned problems, a small-signal model of MC-PMSG through the LCC-HVDC transmission system is erected by using the modularization modeling technique. The eigenvalues are used to study the participation of the MC-PMSG and LCC-HVDC in each SSO mode of the system and the consequence of system parameter changes on SSO damping characteristics. The mechanism of LCC-HVDC grid connection consequence on the SSO damping is analyzed by the damping reconstruction method. The results indicate that an SSO mode in the system is dominated by MC-PMSG, synchronously participated by LCC-HVDC. LCC-HVDC provides negative damping for this SSO mode. When the proportion of the MC-PMSG in the hybrid wind farm increases, the capacity of MC-PMSG increases or the short circuit ratio decreases, the proportional coefficient of the LCC-HVDC constant current controller increases, the integral coefficient of the wind turbine GSC outer loop decreases, or the DC capacitance increases, and the SSO damping increases. The PSCAD/EMTDC electromagnetic transient simulation is used to validate the validity of the theoretical analysis.