The principle of operation of the traditional Pound-Drever-Hall (PDH) method for laser frequency stabilization is analyzed. Based on the principle of quadrature demodulation, a scheme of PDH laser frequency stabilization is designed, in which both sine and cosine signals with the same frequency of 10 MHz are generated simultaneously by making use of a direct digital synthesizer. The sine signal is divided into two parts, one used to drive an electro-optic modulator to produce the phase sidebands, and the other together with the cosine signal used as the reference signals for the phase demodulation. The phase- modulated laser beams are coupled into the reference Fabry-Perot cavity, and the optical heterodyne interference signal is detected by a photo-detector, whose output is mixed respectively with the two orthogonal reference signals to get the two quadrature components of the error signal after low-pass filtered. By the A/D conversations, the two quadrature components are transmitted to the microprocessor to perform the algorithm of orthogonal phase sensitive detection so that the error signal of the PDH frequency- stabilized system is obtained. A system of the PDH laser frequency discrimination using quadrature demodulation method is established and investigated experimentally, and by linearly sweeping the cavity- length of the reference Fabry-Perot cavity, a curve of frequency discrimination is observed, with a sensitivity of 1.82 V/MHz and a maximum frequency change of 5.48 MHz. Experimental results show that the scheme of the PDH laser frequency stabilization system using the quadrature demodulation method is indeed feasible.