The feedwater flowrate is one of the important parameters in the thermaldynamic performance test of steam turbines.On the basis of the conventional heat balance,the matrix calculation model is constructed with the mapping relations between the feedwater flowrate and condensated water flowrate at the deaerator entrance .The model is strongly versatile and easy to be programmed.Furthermore,it effectively avoids the tedious iterative process in the recommendation methods by ASME PTC6 standard and is conveniently applied to the performance test calculation of steam turbines.