Abstract: A 3D numerical simulation was carried out on inner flow in a 90° circular-sectioned bend with fore-end valve using large eddy simulation (LES) method, so as to obtain the flow field characteristics in different sections and the vortex structure in different radial cross sections at full open state of the butterfly valve, which were subsequently compared with particle image velocimetry (PIV) method. Results show that the LES method can well simulate the inner flow field in curved bend, and its result fits well with that of actual experiment; the influence of disturbance from butterfly valve on the inner flow field is relatively high in the area 20 mm above the curved bend center section, where the high speed region moves rearward; vortex structure is found in each section at angle θ=0; the vortex structure at outer side of curved bend is more obvious than at the inner side, and its position is relatively fixed.