Abstract: To study the inner fluid field effect caused by guide blade outlet side position of reactor coolant pump in two-phase condition, three dimensional software Pro/E, non-structural mesh software ICEM, Reynolds time-averaged N-S equations, standard k-ε turbulent model, and CFD software CFX were used to calculate the three-dimensional turbulent flow of nuclear model pumps with different guide blade outlet side position. The void fraction, two-phase relative velocity distribution in the center section of vane and volute are analyzed. The results show that the effect of different guide blade outlet side position to the performance of reactor coolant pump is obvious. It revealed that the flow performance is best when guide blade outlet side is in the centre vertical plane of volute. Research results reflect the internal flow field characteristics of reactor coolant pump in a certain extent, and it also could provide the beneficial reference of the place of vane in the volute of nuclear reactor coolant pump.