Particle-in-cell simulation is used to illustrate induced chirp in the laser wake-field generation experiment. The evolution of the laser pulse characteristics and the wake-field amplitude is investigated numerically. The local frequency of the laser pulse is influenced during wake-field excitation. The numerical result shows that the negative Gaussian chirp profile is the mainly induced chirp throughout the laser pulse. Hence, the induced negative Gaussian chirp has a significant influence on wake-field generation and consequently on the acceleration gradient in the wake-field acceleration
