The phase-matching for nonlinear optical crystal,the nonlinear phase matching angle, effective nonlinear coefficient, walk-off angles, permitted angle, and permitted wavelength are obtained in type-Ⅰ and type-Ⅱ phase matching in ultraviolet (UV) nonlinear optical crystals CsLiB6O10(CLBO) and K2Al2B2O7 (KABO) by detailed theoretical simulation. Through analysis and comparison, the phase matching characteristics of the second harmonic generation in the crystals are discussed when the wavelengths of the basic frequency lights turn continually.