In order to study the subsynchronous oscillation problem of the directdrive permanent magnet synchronous wind turbine generator, a typical mathematical model of wind power system was established. Based on the traditional eigenvalue analysis method, the state variables corresponding to the eigenvalues of system oscillation mode were identified intuitively and accurately by using the homotopy function instead of the participation factor method. On this basis, the influence of corresponding parameters of state variables on the eigenvalue of system oscillation mode was further analyzed. Finally, time domain simulation was carried out on the PSCAD/EMTDC platform. The results showed that the outer ring integration coefficient of DC voltage control and the inner ring proportionality coefficient of current control influenced the subsynchronous oscillation of system greatly.