A crystal oscillator and a phase noise reduction method thereof are provided. The crystal oscillator includes a crystal oscillator core circuit, a bias circuit coupled to an output terminal of the crystal oscillator core circuit, a pulse wave buffer coupled to the output terminal of the crystal oscillator core circuit, and a phase noise reduction circuit coupled to the output terminal of the crystal oscillator core circuit. The crystal oscillator core circuit may generate a sinusoidal wave. The bias circuit may provide a bias voltage of the sinusoidal wave. The pulse wave buffer may generate a pulse wave according to the sinusoidal wave. The phase noise reduction circuit may provide an alternating current (AC) ground path for noise on the bias voltage according to a reset pulse, wherein a position of the reset pulse is set by a control voltage on a control terminal of the phase noise reduction circuit.