Abstract: When the direct-drive permanent magnet synchronous generator (D-PMSG)-based wind farm is close to the rectifier station of line-commutated-converter based high voltage direct current (LCC-HVDC), the mechanism and characteristic of sub-synchronous interaction between them are not clear. With the existing analysis methods, it is difficult to reveal the disturbances transfer process and coupling relationship between subsystems. To solve the above problems, the linearization model of the D-PMSG-based wind farm integrated with LCC-HVDC system was established. Based on the closed-loop transfer function diagram of the system, the transfer path of sub-synchronous frequency disturbance between D-PMSG-based wind farm and LCC-HVDC was shown. Then, the influence of subsynchronous interaction on sub-synchronous oscillation (SSO) mode damping was separated by damping reconstruction, and the influence of controller parameters on SSO mode damping was analyzed. The results show that the SSO mode dominated by DC capacitor of D-PMSG has instability risk. The disturbance transfer path between D-PMSG-based wind farm and LCC-HVDC presents an "8" type coupling relationship, which leads to a sub-synchronous interaction between them. When the proportional coefficient of the D-PMSG outer loop or LCC-HVDC constant current controller increases or their integral coefficient reduces, the SSO mode damping increases.