The bandwidth of three wave mixing optical parametric amplifiers has been investigated. The general mathematical models for evaluating parametric bandwidth and gain bandwidth of three wave mixing parametric amplifiers are developed via three wave noncollinear interactions, the models take into account crystal length, noncollinear angle, group velocity, group velocity dispersion and gain coefficient effects. The results show that the bandwidths are mostly limited by the group velocity mismatch between the signal and idler. Therefor, for any a three wave mixing parametric amplifier, the widest bandwidth can be obtained by choosing noncollinear angle, crystal length and pump intensity, and the super broad bandwidth gain can be realized.