The 25WZ1-12 vortex self-priming pump test prototype was developed. Through the experiment of type and the external characteristics of the variable rotational speed, performance curves, such as qv-H and qv-η, were obtained. The curve conversion for qv-H meets the proportion law of similar theory, but the qv-NPSH curve conversion does not satisfy the cavitation affinity law for the vortex pump. The flow channel field was measured with 5hole probe, to gain the distribution of flow static pressure ps, equivalent vre radial velocity and equivalent circumferential velocity vue at the various pump rotational speed. By analyze the test data, the relation between the external characteristic and the internal flow was discussed, also the type and location for the cavitations of the vortex pump was presented. 