The new computer model of the MOCVD process developed by the author consists of three basic parts: the gas flow model (giving the velocities and temperature distributions in the gas phase), the model of changes of concentrations of the active species in the gas phase (influenced by gas phase reactions and overall gas motion and temperature), and the model of the crystal growth process itself. This paper presents the solution of the first of the mentioned problems: the model of the gas flow in horizontal MOCVD reactor.