Abstract: Based on the special application of 90° elbow pipe in the 10 MW High Temperature Gas-cooled Reactor (HTR-10), the large eddy simulation was used to compute the complex flow field in 90° elbow pipe. The time-averaged results were compared with the experimental results and the RANS results. The pressure fluctuation signal of the specific test point on intrados and extrados was processed by Fourier transform to get the power spectral density. Under the influence of impact effect, flow separation and the secondary flow, the pressure fluctuation behaves differently on intrados and extrados. The pressure fluctuation on intrados is caused by flow separation and vortex-shedding, and the maximum fluctuation amplitude occurs at the bending angle of 50°. On extrados, it is induced by the impact effect, and the maximum fluctuation amplitude occurs at the bending angle of 12°.