In pressurized water reactor nuclear power plants, fuel assemblys may bend due to thermal expansion and radiation growth when subjected to excessive axial compression force. The bowing of fuel assemblies may have a certain impact on the safe operation of pressurized water reactor nuclear power plants. To quantitatively evaluate the impact of fuel assembly bowing on the thermal margin of a pressurized water reactor, this paper proposes a refined microchannel model and analysis method for quantitatively calculating the effect of assembly bowing. For a million kilowatt pressurized water reactor, a quantitative analysis and calculation of the DNBR at the edge of the assembly caused by fuel assembly bowing were carried out. The results show that based on the current operating experience of assembly bowing data, fuel assembly bowing will not impose additional penalties on the thermal margin of the core. The research results indirectly demonstrate the conservatism of an envelope radial power distribution, which can provide new ideas and references for evaluating the bowing effects of fuel assemblies.