Abstract: The aerodynamic optimization of a transonic fan rotor was implemented by controlling the BVF(boundary vorticity flux) distribution on rotor blade. A novel objective function of torque associated with BVF was used to optimize the blade configuration. The physical sources of separated flow could be probed on r otor blade through the BVF diagnosis, which was a novel diagnosis method based o n local dynamics. The shock structure was showed clearly on the rotor blade in th is diagnosis method. Although the torque of the optimized rotor was increased, t he shock strength was decreased and the separated flow was controlled better, as the BVF distribution was better than before. The results of 3D CFD(computationa l fluid dynamics) analysis indicate that not only the total pressure ratio of r otor is increased by 7.69%, but also the adiabatic efficiency is increased by 1 .92% too. The optimized rotor has a higher performance over a wide range of mass flow. The optimization method based on BVF can play an important role in the optimization design of fans/compressors.