Based on an overall consideration of the frequency shifts caused by rubidium isotopes, pressure broadening and hyperfine splitting, a physical model is established to compute the hyperfine splitting structure of rubidium D1, D2 lines. The influence of buffer gas pressure and the cell temperature on the optical cross section of rubidium D1 and D2 lines is analyzed quantitatively, a group of optimized parameters about line shape and bandwidth are obtained. The good agreement between the simulation and the experiment shows the model provides an effective way for understanding the pressure broadening mechanism of alkali atom D1 and D2 lines and matching the bandwidth of D2 absorption line with the diode laser pump source.