This paper describes a method of designing a thyristor frequency converter for a source of induction heating, which converts three phase input power of power frequency to single phase high frequency power without using the intermediate D.C. link. How to determine the circuit constants and the rating of necessary devices such as inductors, capacitors, and thyristors is described with circuit analysis. This design is carried out by the combination of calculating some approximated mathematical expressions and using computer simulation. It is shown that this method is successful in quick determination of parameters.