In this paper, we report some results on inverse opal photonic crystal and two-dimensional periodically poled lithium niobate photonic crystal. At first the process of infiltrating TiO2 into SiO2 Opal was systematically studied. Because of the infiltration of TiO2 the gap of SiO2 Opal was shifted to longer wavelength and a maximum shift of 62 nm was observed. Furthermore, an inverse TiO2 Opal with larger filling fraction, ~ 12%, was fabricated, whose band gap in the G-L direction located in the ultraviolet region (~380 nm). Then two-dimensional nonlinear photonic crystals of lithium niobate with uniform square lattices were fabricated by applying external electric field. The variations of second-harmonic output with crystal temperature, incident angle and reversed duty cycle were measured. Red, yellow, green, blue, and violet coherent radiations were generated in the nonlinear photonic crystal with rectangular lattice in the collinearly and non-collinearly quasi-phase matching geometries. The results showed that two-dimensional nonlinear photonic crystal could be used to generate various colors simultaneously and efficiently along different directions.