A frequency jitter generation circuit having a voltage generator and an oscillator circuit is provided. The voltage generator receives an input voltage and converts the input voltage into an upper reference voltage output to the oscillator circuit. Voltage level of the upper reference voltage is varying. The oscillator circuit is coupled with the voltage generator. Voltage level of a reference voltage in the oscillator circuit is oscillated between the upper reference voltage and a lower reference voltage to generate a frequency signal with a jitter based on the variation of the upper reference voltage.