In this paper, the cavitating flow and pressure fluctuation in the tip region were simulated based on Delayed Detached Eddy Simulation (DDES). The high-speed photography and transient pressure mea-surements were employed to capture the cavitation structures and pressure fluctuation. The numerical results show a reasonable agreement with the available experiments. The maximum errors of head and efficiency are 2.9% and 2.2%. The impeller rotation dominants the tip pressure field, with some obvious high-frequency components induced by the cavitating flow. Increasing the flow rate from 0.8Q(opt) to 1.2Q(opt), the amplitudes of the frequency domain in P2 decrease from 0.13 to 0.08. There are more harmonic-frequency components at 0.8Q(opt), including 5BPF, 6BPF, 7BPF. Suction-side-perpendicular cavitating vortices (SSPCVs) appeared in severe cavitation conditions, which leads to the collapse of the triangular cavitation cloud. The spatial-temporal evolution of SSPCV was divided into three stages: Generating stage, Shedding stage, and Dissipating stage. The pressure fluctuates significantly in the flow passage caused by SSPCV. The amplitudes of dominant frequency in P3 vary from 0.031 to 0.089, as the cavitation number decreased from 0.582 to 0.231. In particular, there is an obvious low-frequency N* = 0.5 shown in the frequency domains of P2 and P3. (C) 2020 Published by Elsevier Ltd.