It′s unavoidable that collinear and noncollinear interactions in the process of optical parametric generator. The quasiphasematched conditions of collinear and noncollinear optical parametric generator are analyzed and the deflection angle is achieved. The curves of the dependence of output gain on phasemismatching are obtained by analyzing and calculating the gain of optical parametric generator. The signal spectra width is worked out in the range of phasemismatching and the curve of signal bandwidth along with the signal wavelength is obtained by numerical calculation. All these findings bear certain guiding significance to the production of the highquality optical parametric generator with high gain, high conversion efficiency and narrow bandwidth.