The influence of wave-front-distorted pump pulse on the beam quality of the amplified signal pulse in the non-collinear optical parametric amplification (OPA) is numerically simulated.The results indicate that diffraction and walk-off effects degrade the signal beam quality via different physical process when the wave-front of pump laser pulse is distorted seriously.Walk-off effect is the main factor to degrade the beam quality of the signal pulse when OPA works in linear regime.The sunken-center of spatial beam shapes induced by oversaturation of OPA play the dominant role in the degradation of beam quality when OPA works in oversaturated regime.