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Abstract-The paper presents an interesting method for the derivation of transfer function from passive RCLnetworks (Resistance, Capacitance and Inductance) with a ladder structure. In this paper, circuit network modeling methodology is extended into thermal system. In order to apply directly the methodology to thermal system, firstly pseudo bond graph method, as an intermediary, is utilized to depict the model of thermal system, secondly the model is transformed into its equivalent circuit diagram, finally according to the methodology, the mathematical model in format of transfer function of thermal system can be rapidly obtained by observing circuit diagram alone. Through a modeling example of heat transfer in building envelope wall, it has been verified that the mathematical models obtained by circuit network modeling methodology and pseudo bond graph method are identical, but this methodology has the advantages of simplicity, convenience, rapidness and intuitiveness in manual derivation of transfer function of thermal system.