The invention relates to a system based on gas-steam combined cycle and a rapidly modeling method thereof. The rapidly modeling method is characterized by comprising the following steps: 1) creating asystem model framework comprising a client-side and a server-side equipped with a database and an MATLAB module; 2) saving an algorithm model of a gas-steam combined cycle system in the MATLAB moduleand encrypting the algorithm model; 3) determining different unit parameters of the gas-steam combined cycle system and sending the different unit parameters to the client-side by inputting the different unit parameters into the client-side; 4) calling the algorithm model by the MATLAB module to carry out simulating calculations and returning calculation results to a database; 5) sending the returned calculation results to the client-side by the MATLAB module and displaying the results through the client-side; 6) obtaining technical and economic indicators of the gas-steam combined cycle system according to the obtained calculation results in order to support design and planning of a power grid source and optimized operation of fuel gas and thermal power plants. The system based on gas-steam combined cycle and the rapidly modeling method thereof can be widely applied to rapid modeling.