From two dimensional steady state plasma fluid equations, assuming a balance of radial electron thermal pressure and radial pondermotive force in the cyliudrical symmetrio distribution of electron density in laser irradiated region, the analytical results have been deduced of radial electron density dip structure in the laser field region and the axial electron density profile steepening near the critical density due to the pondermotive force. The analytical results are consistent with the experimental results measured by a 266 nm UV optical pbobe.