The invention provides a reference clock determination method and a reference clock determination device. The reference clock determination method comprises the steps as follows: a logic device receives a local clock and an external clock, discriminates the phase according to the frequency of the local clock and outputs a phase discrimination value; a processor reads a phase difference according to the phase discrimination value and outputs a digital voltage value; a digital-to-analog converter converts the digital voltage value into an analog voltage value and outputs the same; a voltage-controlled oscillator adjusts the frequency of the local clock output by the voltage-controlled oscillator according to the analog voltage value, and locks the external clock; and the local clock is usedas a reference clock. Based on the technical scheme provided by the invention, phase noise deterioration and frequency jitter of the local clock caused by the accessing of the external clock are avoided, and particularly, the higher accuracy and stability can be brought to the system.