A supercritical 600 MW thermal power unit was taken as an object to study the indirect modeling strategy for thermal power units. The sub-space identification method was adopted to solve the discrete system model step by step. Firstly

the intermediate point temperature model

the main steam pressure model and the load model was built up. Then

the main steam temperature model was established by using the intermediate point temperature as the input variable. The obtained model overcomes the disadvantage of inaccuracy of the main steam temperature model in direct modeling. The effect of main adjustment of the boiler on dynamic characteristics of the unit was studied. Finally

the separate models were integrated into the overall unit model.The obtained overall model can better reflect the dynamic characteristics of the unit under rated working conditions and has good fitting degree. The result has practical value for researches on controllers in supercritical units.