The invention provides a quartz crystal series connection resonant frequency test method, comprising the step of applying a first sinusoidal signal and a second sinusoidal signal, having the same frequency to a Pi network and a balancing resistor, and inserting the quartz crystal into Pi network. Accordingly, the phase of the first sinusoidal signal is a first predetermined angle ahead of the second sinusoidal signal, and the output frequency of the first sinusoidal signal and of the second sinusoidal signal changes from low to high. When the phase difference between the first output signal of the Pi network output end and the second output signal of the balancing resistor output end is zero, the frequency of the first sinusoidal signal and the second sinusoidal signal is the first predetermined angle frequency of the quartz crystal. Accordingly, the phase of the first sinusoidal signal is a second predetermined angle behind of the second sinusoidal signal, and the output frequency of the first sinusoidal signal and of the second sinusoidal signal changes from low to high. When the phase difference between the first output signal and the second output signal is zero, the frequency of the first sinusoidal signal and the second sinusoidal signal is the second predetermined angle frequency of the quartz crystal. The series connection resonant frequency is calculated based on the first and second predetermined angle frequency.