In the present work, the microcanonical distribution of particles in the phase space is considered. This the simplest selfconsistent distibution for a charged particle beam in a linear transverse electric field. Commonly, density of this distibution is described by the delta-function. But such aproach is not correct as particles are distributed with some density on surface of a 3-dimensional ellipsoid in the 4-dimensional phase space. Therefore, covariant approach developed previously was applied. According to this approach, particle density on the ellipsoid surface is described by a diffential form of the 3-degree. Numerical simulation of the microcanonical distribution is carried out. The results show that the distibution is conserved approximately when particles move.