Abstract: High frequency spatial modulation induced by Fresnel diffraction of broadband nanosecond chirped laser pulse were studied. It shows that the hundreds-nm broadband pulse has some effects on Fresnel diffraction, while the tens-nm one has hardly any. Moreover, three B-integral expressions and the fast gain frequency of tens-nm broadband nanosecond chirped laser pulse were studied, and compared with the nonlinar experiments of narrowband pulse and chirped pulse stacking on Technical Intepration Lines facility. The results reveal that, the maximal B-integral or the weighted average B-integral can better reflect the nonlinear self-focusing phenomenon, and there are no distinct differences between the narrowband and the tens-nm broadband nanosecond laser pulses with respect to the fast gain frequency.