The design method of small-flow high-head centrifugal-vortex pump was presented.This pump,configured with 1nducer,complex-centrifulgal impeller and open-vortex impeller,was put torward to deliver gas-liquid two-phase mixture.An HTB-5/60 type sample pump was developed and tested on a closed-loop test rig.Experimental studies on perfbrmance and cavitation tests tor gas-hquid two-phase mixture were camed out compared With pure-water experimental results.Also the effect of gas phase on pump was analyzed and discussed.The experimental results show that performance and cavitation characteristics of the sample pump deteriorates progressively with increasing volume fraction of gas.When the total capacity QmiS between 4.5 m3·h-1and 6 m3·h-1 and the gas flow rate qg below 0.66 m3·h-1,or qg/Qm is lower than 15%,the characteristic curves are approximately parallel to those in pure water test,but the perforh~deteriorates sharply until an abrupt flow-cutting at a critical volume fraction of gas.This pump is found suitable for transporting gas-liquid two-phase mixture when working around rated capacity of 5 m3·h-1 with qg/Qm below 15%.