A scheme employing a lens array and the technique of smoothing by spectral dispersion is presented for uniform irradiation on targets in inertial confinement fusion. Quasi-near field spots with a profile of sharp edge and flat top can be obtained with a diffraction-weakened lens array, while the speckles imposed on the spot by beamlets interference can be smoothed by spectral dispersion. Simulation results indicate that this scheme is a good candidate for improving the irradiation uniformity. The dependence of the smoothing performance on the characteristics of phase modulation and dispersion is further discussed, and it is found that parameters of the system of spectral dispersion and lens array must be chosen carefully to make optimal compromise between uniformity and usable energy of the laser beam.