Abstract: In the first 100% rated power operation of China Experimental Fast Reactor (CEFR), there is a certain gap between the practical electric power and the design value. The analyses were done to identify the main factors impacting the generation efficiency. The operation data from the field and the design information from the turbine manufacturer were used as the basis for the following calculation. The internal efficiency for steam turbine was modified, the approximate thermodynamic process curve of steam turbine was drawn, and the enthalpy of the extraction steam was acquired based on the curve and using the actual extraction steam pressure. The extraction steam flow was obtained through the heat balance calculation based on the energy and flow conservation equation of the deaerator and the low pressure heaters. The calculated value of the steam turbine power was obtained using the power calculation equation of steam turbine. By comparing the calculated value with the actual value, it is concluded that the main steam parameter is not up to the standard, which is the main factor that affects the power generation capacity of CEFR steam turbine.