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In order to investigate the influence of cavitation on pressure pulsation in ultralow specific speed centrifugal pump, combining experimental and numerical simulation methods, the frequency domain and amplitude characteristics of pressure fluctuation were analyzed at different positions in an IB 50-32-250 ultralow specific speed centrifugal pump with different net position suction head available (NPSHa). The results showed that cavitation can induce low frequency and broadband frequency fluctuation. When there was no cavitation, the pressure pulsation in impeller flow passage was mainly related to the impeller rotation frequency and its harmonic frequency;while in the volute, because of the interference between impeller and volute tongue, the main dominant frequency of pressure pulsation was the blade pass frequency and its harmonic frequency, and the pressure pulsation near tongue was the strongest. With the decrease of NPSHa, pressure fluctuation of most monitors in the impeller passage was weakened, but that in the edge of cavitation zone was enhanced. The main frequency of pressure pulsation near the impeller inlet was changed from rotation frequency to 1/6 rotation frequency at the critical cavitation. Besides, the developing ununiformity of flow field in volute caused the amplitude of pressure fluctuation strengthened. The main frequency of the volute and pump outlet was still blade pass frequency, but 1/6 rotation frequency became the secondary frequency with larger amplitude. The research can provide necessary basis for the reduction of vibration and noise intensified by cavitation in the ultralow specific speed centrifugal pump.