© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. A planar polymer brush of arm-grafted polymer stars subjected to external deformation is studied theoretically We propose a simple mean-field model of the star brush that takes into account segregation of the brush-forming stars in two populations: (i) those with weakly extended arms and (ii) those with a very strongly stretched grafting arm (stem) and all free arms extended towards brush periphery. The polymer density profile in the brush is assumed to have a "two-step" shape. Stars in the extended population are assumed to be equally stretched, the position of extended stars' branching points sets the boundary between two parts of the brush. We show that the theory quantitatively accurately describes earlier numerical results obtained with Scheutjens-Fleer numerical self-consistent field (SF-SCF) approach for free (non-deformed) star brush. We study compression of a star brush by an impenetrable plane by using two complementary models, the SF- SCF approach