Abstract: Subcooled boiling heat transfer simulation of PSBT full scale 5×5 rod bundle with uniform-axial power distribution (APD) was carried out with wall heat flux partition method. Axial sub-channel averaged parameter analysis along axial orientation among different sub-channels was studied. It is found that lower mixing effect, observed in corner and lateral sub-channels, makes negative contribution to heat transfer. But this effect is eliminated due to the lower power of cold rod (CR). The difference of parameter distribution is found among sub-channels. The mixing process among sub-channels in the central diagonal of mixing is strengthened due to the sustaining transverse flow induced by the vanes, which leads to an increasing heat transfer in these sub-channels. In the corner sub-channels, notable difference is observed. The wall superheat of hot-rod (HR) is higher than that of the CR. The HRs, which locate outside of the central diagonal of mixing, have a higher wall superheat than other HRs.