The spectral bandwidth and gain of PPLN based optical parametric amplification (OPA) with different noncollinear geometries have been investigated. The spectral bandwidth and gain is determined by expanding the wave-vector mismatch in a Taylor series and retaining terms through second order. The calculation takes into account the effects of grating period, noncollinear amplification geometry, crystal’s length and pump intensity. The results show the grating period of PPLN and the noncollinear geometry has effects on the spectral bandwidth. The characteristics of gain bandwidth are similar to those of parametric bandwidth; they are all greatly enhanced on the condition of broadband amplification. Compared with the increase of pump intensity, the gain can be effectively improved by increasing crystal′s length, while the grating period and the noncollinear amplification geometry almost have no effect on the gain.