In view of the relatively slow rotary speed and relatively large number of poles of hydro power generators， also considering the difficulties in realizing accurate measurement of power angle， an accurate power angle measurement method is proposed to handle the special characteristics associated with the large teeth and the uniform teeth. The new measurement method can make full use of the mechanical errors between the two teeth to obtain the matching space width. It also uses the frequency tracking method to solve two problems associated in the measurement process:（1） the measurement is sensitive to the frequency disturbance in the initial phase angle verification stage， and（2） the power angle measurement accuracy difficulties with direct measurement method for various types of teeth. The general idea and software flowchart of the method are introduced. The power angle measurement curves recorded in Tianhuangping pumped storage power station in Zhejiang Province are given with satisfactory measurement results.