During the fabrication of quasi-phase-matched (QPM) devices, errors of periodic structure are usually inevitable.The errors result in the deviation of the actual periodic domain length from the theoretical value. In this paper, wenumerically analyse the influence of errors on the quadrature squeezing performance of a degenerate optical parametricamplifier consisting of QPM devices. It is shown that errors significantly degrade the squeezing degree of the quadraturesqueezed light. Due to the presence of the errors, the relative phase between the signal and the pump field for obtainingthe maximum squeezing depends on the propagation distance of light in the crystal and the pump power.