In negative-index materials(NIM) for signal wave and positive-index materials(PIM) for pump wave and idler wave in the structure of PIM/ NIM/PIM,based on three-wave mixing optical parametric amplification,according to the phase matching,there is a maximum noncollinear angle(MNA) when these wavelengths of signal wave and pumping wave are given. The curve of the MNA vs the signal wavelength has been discussed in detail. A analytical expression of spectral bandwidth is obtained through retaining term of first order(when expanding circular frequence of wave vector in Taylor series). Making use of the analytical expression,one has researched this laws of the parametric bandwidth vs the wavelength of signal light,pump light and the noncollinear angle through the method of numerical calculation. Results show that the parametric bandwidth first increased and later diminished with increase of the signal wavelength for the fixed pump wavelength,that is,the maximum parametric bandwidth existed;the parametric bandwidth gradually increased with increase of the noncollinear angle for the fixed pump wavelength and signal wavelength. Besides,the parametric bandwidth also increased with increase of the pump-light intensity. This study provides a basis for investigating optical parametric amplification of negative-index materials.