Abstract: In order to study the effect of blade inlet position on flow characteristics of nuclear reactor coolant pump under gas-1iquid two-phase condition, three different schemes of inlet position had been designed and simulated on steady and unsteady stage under gas-liquid two-phase condition. The analysis of the results shows that the blade inlet of the nuclear coolant pump protrusive properly, can be good to keep the stability of the pressure boundary in the LOCA（Lost of Coolant Accident） event. But the protrusion can exacerbate the degree of blade twist, and lead to a large number of bubbles accumulating on the suction surface. The blade inlet offsets backwards, easy to cause strong jet trails and large amplitude pressure pulsation at the outlet of the impeller. By the comparative analysis, the scheme B turns out to be the optimal solution. The external characteristics of the optimal model prototype, based on the simulation, was tested on different inlet gas rate conditions. The rustle shows that predicted curve is basically consistent with the experimental one under 0% inlet gas operation condition and the performance meets the design requirements. With the increasing of the gas rate, large deviation appears in the experimental values and simulation values. This is mainly due to the limited test conditions, and the error of simulation results with the experimental results.