The master thesis deals with combined heat and power (CHP) production using the combined cycle gas turbine power plant (CCGT). First the different CHP technologies were described and the main characteristics are pointed out. The thesis is focused on analysis of CHP CCGT system with extraction-condensing steam turbine to provide process heat which is used for district heating. According to actual data on heat demand and also to existing heat production systems a CHP CCGT system was designed and modelled. The model was developed by introducing the linear system of equations of mass and heat balances which has been solved numerically. After obtaining the steady-state solution of the system an off-design scheme has also been developed that enables simulating of the part-load operation conditions. It has been shown that the approach provides a good tool to analyze and study the CHP CCGT system in terms to calculate the most important parameters that should be used for construction.