Abstract: The rotor blade in the first stage of Aachen turbine was added with a fillet structure,and a full three-dimensional viscous numerical simulation was performed to analyze the influence of rotor fillet on the performance of turbine stage and flow fields under the stage environment.The results indicate that the efficiency decreases significantly when the angle between fillet and end wall becomes too small,which should raise more attention in the manufacturing process of rotor blade.The fillet structure decreases the transverse pressure difference near the rotor hub and shroud,and shifts the aerodynamic load to the latter half part of the rotor blade.The fillets at hub and shroud affect the flow field of the rotor mainly at the 0%～55% span and the 70%～100% span,respectively.The upper and lower passage vortexes are close to the midspan of rotor due to the influence of the fillet,leading to increase of the intensity of corner vortex and the loss of second flow near the endwall.