The invention discloses a simple calculation method for variable working condition performance of a steam extraction heat supply type gas-steam combined cycle unit. The method comprises. The method comprises the following steps: building a gas cycle variable working condition model of the combined cycle unit, and calculating gas parameters under variable working conditions according to the gas cycle variable working condition model; correcting gas parameters under variable working conditions; and calculating variable working condition output parameters of the combined cycle unit. According tothe invention, a data and mechanism combined modeling mode is adopted; a component characteristic equation derived from experimental rules and theories is used as a basis; fitting the key parameters and the key coefficients of the equation by utilizing past data of the unit; the application range of the model is widened; the problems that a gas compressor and a gas turbine in gas circulation are difficult to model due to the fact that manufacturers keep performance data secret, and the modeling process of a waste heat boiler is complex are effectively solved. Simple calculation of the variableworking condition performance of the gas-steam combined cycle unit considering universality and high precision is achieved, and an effective means is provided for variable working condition characteristic analysis of the combined cycle unit.