With the increase of grid connected capacity of new energy such as wind power, the large-scale access of wind power in the power grid has brought new challenges to the stability of the system. When the wind turbine is connected to the thermal power system, the mechanism of sub-synchronous oscillation caused by the interaction between wind turbine and traditional thermal power is not clear, so it is worth further discussion. In this paper, the eigenvalue analysis method is used to establish the state space model of wind fire hybrid AC series compensation and VSC-HVDC grid-connected transmission system, and the influence of fan access on the natural oscillation mode of traditional thermal power is studied through comparative analysis. Furthermore, by changing the grid-connected distance and other parameters, the influence of system structural parameters on the sub/super-synchronous oscillation mode caused by the interaction between fan and thermal power is analyzed. On this basis, the influence mechanism and factors of wind power access on traditional thermal power sub-synchronous oscillation under AC transmission and VSC-HVDC transmission are revealed. The correctness of the proposed system is verified by time-domain simulation on PSCAD/EMTDC platform.