The quasi-ste dy density profile determined by the ponderomotive force in a laser plasma is studied. The dependences of the local density scale length, the lengths of upper and lower density shelves and the average density scale length at lower shelf on the incident light intensity and time are derived. It is shown that after the quasi-steady state is reached, with the lapse of time the lengths of upper and lower density shelves and the average density scale length at lower shelf rise, and the density scale length, at lower shelf rise, and the density scale length in the critioal density region increases slightly.