Based on the Fokker-Planck equation along with laser propagation equation, a theoretical model that describes the ultrashort-pulse laser propagation characteristics and breakdown in dielectrics is established. Using this model, the conduction band electron densities and the electric field intensities at different positions in a dielectric material at different time are calculated. The variations of reflection, transmittance and energy deposition rate with input laser energy density are discussed. With the threshold conduction band electron density criterion, the breakdown depth in the material under varying laser energy density is calculated, which is found to increase first with laser energy density, and then to decline after reaching a maximum value. Effect of the spatial distribution of laser energy deposition on breakdown depth is analyzed. Meanwhile, the maximum value of breakdown depth is found to decrease as the laser pulse duration becomes shorter.