In order to avoid adverse effect arisen from group velocity mismatch in femtosecond optical parametric amplification (OPA), a method that compensates completely the group velocity mismatch among three waves is presented, by tilting simultaneously wave fronts of pump and signal pulses, for femtosecond OPA in β-BaB2O4 (BBO) type-Ⅱ collinear phase-matched configuration. When the group velocities of three waves are matched, the variations of the phase-matched angle and the wave front tilting angles of pump and signal pulses with the signal wavelength are calculated theoretically, and the effects on the pump beam size and the parametric bandwidth are analyzed. The results indicate that this method not only can match completely group velocities among three waves, but also can achieve maximal parametric bandwidth for continuous tunable femtosecond BBO OPA. In addition, for increasing parametric gain, it is very importance to appropriately choose the pump beam size.