Abstract: On the basis of preliminary analysis on the conditions, traditional methods and characteristics of the reactor-mechanical-electricity matching of 320 MWe unit in Qinshan Nuclear Power Plant, with the application of the current advanced and efficient thermal hydraulic calculation, pipe resistance calculation and heat balance calculation software, taking the required power of the unit capacity expansion and retrofitting as the goal, on the premise of ensuring that the nuclear island reactor power does not exceed the enhanced working condition power, for different pressures and flows of main steam at the outlet of steam generator (SG), according to a certain step length, and considering different feed water temperature, reasonable main steam pipe resistance, optimized cold end parameters, combined with the current advanced design and manufacturing technology of steam turbine generator unit, the thermal hydraulic calculation and thermal balance iterative calculation have been carried out to form the optimized inlet main steam parameters of steam turbine and generating power of unit. While meeting the power target, the efficiency of the unit has also been improved. After the unit capacity expansion and retrofitting, the parameters and performance of the reactor-mechanical-electricity equipment can be better matched, and the operation of the unit is more safe, stable and economical.