The possibility of stable location of dust grains in a comet atmosphere with weak dust content is studied on the basis of the simulation of the hydrodynamical spherically symmetric gas flow, if Knudsen boundary layer of a comet nuclear is taken into account, at heliocentric distances from 1.6 to 3.0 a.u. We consider two types of surface sublimation, namely, a clean homogeneous surface of water ice and that covered by a porous mineral crust. With the use of the phase plane method it is shown that there are two specific points in a comet atmosphere for centimetre-sized dust particles and one of the points is a point of stable equilibrium. A relationship between this point position and dust grain sizes is found. Variations of the density and shape of grains as well as the size distribution result in initiation of a stable equilibrium zone. Its location depends on the size of a comet, distance of a comet from the Sun, and the state of the nuclear surface of a comet. For comets of size 2.5 km at 2 a.u., this zone is positioned at distances from 10 to 1000 km and corresponds to the dust grains of size from 4.5 down to 0.5 cm and of density 1 g/cm³.