We previously proposed a Magnetic-Flux-Control transformer (MFC transformer). The MFC transformer has simple construction and high reliability because it consists of only a core and its windings. The MFC transformer can control output voltage and net inductance easily and continuously.For wide application and practical use, it is necessary to establish a design method for the MFC transformer. In this paper, we present an analytical method for the MFC transformer using Reluctance Network Analysis (RNA) and examine the characteristics of an MFC transformer.