The present invention belongs to the technical field of lasers, and particularly relates to a periodically poled crystal and an optical parametric amplifier. The present invention provides a periodically poled crystal, including a first nonlinear region, a linear region and a second nonlinear region, wherein the first nonlinear region and the second nonlinear region both have periodically poled structures. The optical parametric amplifier having the periodically poled crystal can separate the idler wave from the signal wave besides achieving the basic function of optical parametric amplification because the by-produced idler wave transmits in a direction different from the directions that the signal wave and the pump wave transmit, and therefore the energy reflow is suppressed when the optical parametric amplifier has reached saturated amplification, and the performance of the optical parametric amplifier is significantly improved.