Modelling of evolution of dusty shells around post-AGB star of 0.598 M⊙ mass has been performed by means of the Yorke's hydrodynamical code. In this code dust and gas are treated as two separate components coupled by friction, and the spectral appearance of the model is computed by solving the angle and frequency dependent continuum radiation transfer problem. Calculations were carried out for dust composed of silicate grains. The emergent spectrum of the model has been convolved with the IRAS photometric band profiles to construct theoretical tracks on the IRAS two-color diagram.