The balanced homodyne detection technique is an important method to detect the quantum light field. The signal light injected into the phase sensitive optical parameter amplifier (OPA) is phase modulated. The output squeezed light of OPA is detected by the balanced homodyne detection system. When the phase sensitive OPA is operated at parametric amplification and deamplification respectively, we can judge which quadrature component of the quantum light field is measured by observing the modulation signal. We can demodulate the phase modulation signal to achieve the error signal, which is used to lock the relative phase of zero between the local and the quantum light fields (corresponding to the quadrature-amplitude of the unknown light field).