Based on the Huygens–Fresnel diffraction integral and Fourier transform, propagation expression of a chirped Gaussian pulsepassing through a hard-edged aperture is derived. Intensity distributions of the pulse with different frequency chirp in the near-fieldand far-field are analyzed in detail by numerical calculations. In the near-field, amplitudes of the intensity peaks generated by themodulation of the hard-edged aperture decrease with increasing the frequency chirp, which results in the improving of the beam uniformity.A physical explanation for the smoothing effect brought by increasing the frequency chirp is given. The smoothing effect isachieved not only in the pulse with Gaussian transverse profile but also in the pulse with Hermite–Gaussian transverse profile whenthe frequency chirp increases.