Driven by the requirement for a fairly accurate and fast simulation of a variable frequency digital controlled flyback converter, this paper develops a control-oriented mathematical model, which retains the essential dynamic characteristics of the real system, but offers significant computational complexity reduction compared to a full modelling approach. In addition to the model simplification, an approach to further improve the simulation speed, through a specific implementation of the differential equation solver, is also considered. To verify the accuracy of the proposed model, different tests with both open-loop and closed-loop flyback converters are performed. The results from both simulation and experiment show good agreement in all the test cases.