A predictor-corrector based eigenvalue spectrum tracing algorithm of time delayed power systems is presented. System eigenvalues without time delay are calculated firstly. Time delays are then gradually increased to get the predictive result by the predictor. Subsequently， an optimal model is used as the corrector to obtain the final result. The WSCC 3-generator 9-bus system is used to validate the proposed method. The results show that it could trace all eigenvalue locus of the time delayed power system precisely. In the study， some bifurcations existing in the time delayed system are found， illustrated and studied， such as oscillation disappearance bifurcation（ODB）， oscillation emergence bifurcation（OEB） and oscillation aberrance bifurcation（OAB）. Furthermore， changes of the system eigenvalue number due to the bifurcations are also discussed.