Abstract: Abstract: The rotor axis locus of the mixed-flow pump is an important graphic sign of rotor vibration state, so it is an effective way to reflect the actual rotor movement condition intuitively. Also, it is an effective research method to prevent the rotor vibration deterioration induced by the hydraulic vibration. In this article, the experimental study on the axis locus of the mixed-flow pump was based on the Bentley 408 data acquisition system under the condition of 0.8, 1.0 and 1.2 times of the design flow rate (380 m3/h). Besides, the rotor original axis locus chart and time domain chart of the mixed-flow pump were obtained in this article with the bi-directional dynamic measurement method. And then, the rotor original axis locus chart and time domain chart were purified with the signal processing and filtering functions of the ADRE Sxp software. The Butterworth filter was used to purify the original signal of the mixed-flow pump. Then, the rotor axis locus chart and time domain chart at one time frequency and double frequency were analyzed. Meanwhile, it also drew the waterfall spectrum diagram of the mixed-flow pump under different flow rate conditions. Those results showed that the flow rate had a great impact on the misalignment and the unbalance of the rotor system. From the results, we could know that the misalignment causes power-frequency vibration while the unbalance causes horizontal vibration. With the flow rate keeping away from the design flow, the vibration was increasing, and the shaft vibration which was caused by hydraulic excitation had peak vibration under small flow rate condition. The fluctuation amplitude of the rotor axis locus chart at one time frequency under the condition of 0.8 time of flow rate was 1.35 times higher than that of the design flow rate. The middle and high frequency vibration force which was induced by the unsteady flow under the condition of low flow rate was the main reason that caused power-frequency vibration deterioration. The fluctuation amplitude of the rotor axis locus chart of the double frequency had the maximum value with the increase of the hydraulic load. This article also adopted the frequency spectrum under different flow rate conditions to analyze the reason. It could be detected that the misalignment increased and the unbalance of the rotor system also became worse than ever when the flow rate value was keeping away from the design point. What was more, the vibration of shaft system also increased with the flow rate changing. The power-frequency vibration was the main component of the shaft system vibration and the double frequency also had great effects on the shafting vibration state, while other low frequencies had little influence on the shaft system vibration. The research results are useful for reducing or preventing the deterioration of vibration effectively, and provide the important reference for the steady operation of the mixed-flow pump under multiple working conditions.