The cyclone-type separator with swirling baffle and bottom take off of clean gas is a patented technique for separating solid particles from gases. Main relative dimensions of the separator are the same as given by Stairmand [C.J. Stairmand, The design and performance of cyclone separators, Trans. Inst. Chem. Eng. 29 (1951), 356-383] for the high efficiency cyclone. The principal part of the construction is the cylinder-shape swirling baffle with the flow gaps cut on its surface. The article presents the theoretical model of the new construction of cyclone-type separator with swirling baffle and bottom take off of clean gas. Calculational model to predict the collection efficiency was based on Leith and Licht cyclone calculational method [D. Leith, W. Licht, The collection efficiency of cyclone-type particle collectors - a new theoretical approach, AIChE Symp. Ser. 68 (126) (1972), 196-206]. The main assumption of the developed model is that the tangential velocity distribution is obtained by superposition of velocity fields generated by tangential gas inlet and rotating motion of the separation baffle. Suggested pressure drop calculational method assumes that total pressure drop consists of five partial pressure drops due to gas expansion at separator entrance, wall friction within the separator, rotating motion of the baffle, gas flow through the flow gaps of the baffle and through the outlet pipe.