Abstract: The self-priming process of irrigation pump is a complex gas-liquid two-phase flow process, with the transient parameters closely related to the self-priming performance of the pump. In order to research the relationship between inner transient flow and explicit transient performances during self-priming period, a self-priming pump typed 65ZB-40 is tested with the NI virtual instrument and LabVIEW used. Through the rapid test and data acquisition system, not only the transient parameters are obtained, but also the transient performances of the pump during self-priming period under different installation heights are tested. The relationships between the instantaneous rotational speed, the pressure, the flow rate, the head, the power, the efficiency and the self-priming time are established. The results show that the pressure variation tendencies at each monitoring point are similar under 6 different self-priming heights. The vacuum degrees at the pump inlet and at the impeller inlet increase with the self-priming heights. The pressure is negative at the reflux hole in the initial self-priming period, but the pressure roars to about 400kpa in the final stage, which indicates that the reflux hole is the main region where the gas liquid mix for the external-mixture self-priming pump. The pressure at the pump inlet is general about 1-2kpa, but it develops to almost 400kpa when the self-priming is finished. The flow rate, the head, the shaft power, the output power and the rotational speed also change obviously at the end of self-priming. The efficiency arrives at its peak when the self-priming is finished. The transient effects are obvious during self-priming period. The experimental results are analyzed and compared with explicit transient hydraulic performances, and the experimental results are in agreement with the theoretical calculations.