Femtosecond laser filamentation has recently emerged as a promising technique to actively create a channel through clouds and fog, thereby providing a revolutionary opportunity to overcome the obstacle of fog-induced attenuation for free-space optical communication (FSOC) in atmosphere. However, the underlying physics remains elusive, which is critical for optimizing time window and efficiency of guiding light in this channel. In this work, the time evolution of the filament-induced channel is investigated under various laser pulse energies and repetition rates. The combined diffusion model is built to reveal the contributions of gas molecules and aerosol droplets in competition of guiding and defocusing effect of the filament-induced channel. The related findings can deepen our understanding on the underlying physics of the air channel induced by the filament, provide insight into the optimizing time window and efficiency of guiding light, and potentially contribute to the improvement of filament-assisted FSOC.