We have theoretically analyzed the characteristics of an optical parametric amplifier system seeded by an optical parametric generation. We investigated the influences of the energy, pulse duration, material dispersion, and the third-order nonlinear effect in β-barium borate. The group-velocity mismatch (GVM) becomes the most important factor for the amplification of bandwidths. Even though tilting the wave front of the pump can decrease the GVM, it seems impossible to generate pulses smaller than 10-fs with 400-nm pumping. However, 10-fs pulses can be achieved with a 30-fs pump duration with pumping at 800nm.