Abstract: In recent years, a new type of sub/super- synchronous oscillation (SSO) occurred in the large-scale wind power system in China. The frequency of these emerging SSO issues gradually changes with time. The exiting phasor measurement units (PMUs) and wide-area measurement system (WAMS) cannot monitor the dynamics of sub/super-synchronous oscillations in wind power systems. To deal with these challenges, this paper investigates impacts of the sub-synchronous and super-synchronous harmonics on traditional PMU algorithms. The root cause of measurement error caused by harmonics is thoroughly analyzed. A new method which can automatically adapt its frequency is proposed to track the fundamental phasor, sub-synchronous phasor and super-synchronous phasor simultaneously. The electromagnetic transient simulations based on a practical wind power system are carried out to validate the effectiveness and accuracy of the improved method.