Abstract: The principle, manufacture and application of periodically poled lithium niobate(PPLN) are introduced in detail.PPLN develops rapidly with the character of effective nonlinear coefficient and it is one order of magnitude higher than that of common bulk crystal. PPLN is manufactured by applying external field, proton exchange and so on. In recent years, its technology and effect iveness of the light to light has made much progress. PPLN can be used to frequency doubling of solid-state laser, parametric oscillation and even to doubling frequency of semiconductor laser. Whether the PPLN is used has become the conclusive factor to develop the traditional nonlinear laser source.