We introduce the continuity equation written in the coordinate space of the orbital elements (e.g. large semi-axis a vs. eccentricity e, etc.) to explore the density evolution of the zodiacal cloud. Emphasis is on those terms of the continuity equation which describe ‘jumps’ of particles in the (a, e)-space due to gravitational scattering of the interplanetary dust particles by planets, which represents one of the leading factors in the dynamical evolution of the zodiacal cloud. In the remainder (div-terms of the continuity equation), one can incorporate the known analytical expressions for the rates of gradual change of orbital elements due to the Poynting-Robertson and solar wind drags (Liou et al. 1995).