Ab initio calculations modelling catalysts of C-Cl bond metathesis were carried out. The complicated catalytic system consisted of three different groups of components - amides, copper complexes in different oxidation states and inorganic support. The results of calculations, in good agreement with experimental data, explain the way of fixing the active catalyst on silica surface, describe geometrical parameters and redox properties of copper complexes with donor ligands, verify some key stages of the proposed mechanism of metathesis.