In recent years，in a broad field DC/DC converter has been applied. However，especially Push-pull type DC/DC converter has some advantage that it can control ripple of input current and make high boost ratio. For these feature，it is suitable for out put voltage of boost ratio solar photovoltaic and fuel cell. However, it has some problem that circuit has not been enoughly analysised and so on. Therefore，it had not been produced. So，the writers have analyzed of feature of Push-pull type DC/DC converter and revealed the feature of Magnetizing current and Magnetic unsymmetrical phenomenon that had not been clear.