Abstract: For indigenous mega-kilowatt class reactor cooling pumps (RCPs) project, the performance characteristics of subject pump based on the scale model of RCPs are fully researched in the specialized experiment system. The pump characteristics under single-phase liquid condition in normal speed case, turbine case, energy dissipation case, rotor locked case and runaway speed case are firstly obtained. Furthermore, the pump two-phase specific operating conditions under the void fraction of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 are studied one by one. Finally, we use the proportion law to sort out the experimental data under multiple pump speeds, and then obtain the change rule of the pump head under different void fractions and different flows. The curve of pump head proportional law on the basis of single-phase liquid has a process of continuous drift and regression with the increase of the void fraction. When the void fraction reaches about 0.7, the drift degree is the largest, and when the fluid changes to single-phase gas, the regression is realized. The above experimental results provide data support for further research of nuclear main pump design and primary circuit safety analysis.