In rotating electrical machine design, the magnetic equivalent circuit based on the reluctance network method seems to be a fair tradeoff between computational time and precision. Therefore this paper deals with a semi-analytical calculation method of the direct and quadrature axis magnetic circuit in Reluctance Synchronous Machines (RSM) by the means of a nonlinear reluctance network. The corresponding non-linear equation systems are derived by forming separated equivalent magnetic networks of the stator and the multiple flux-barrier rotor divided by the air-gap. An adaptive interconnection network to model the air-gap is not needed and as a result relevantly simplifies the analysis compared to conventional reluctance network calculation with one global system. However the analytical calculation model provides results significantly faster than Finite Element Method (FEM) with a sufficient precision and thus is suitable for a first rough design of the RSM.