The ICEM software was used to mesh the model of turbo air classifier and numerical simulation was performed by Fluent software to characterize separation process of potato starch. The effect of parameters such as rotational speed, inlet velocity and number of rotor blades on the cut size were studied. The response surface analysis method was used to optimize process parameters on turbo air classifier. The results indicated that the rotational speed, inlet velocity and number of rotor blades all influenced the cut size of potato starch. The order of effect on cut size was as followed: rotational speed＞inlet velocity＞number of rotor blades. The optimal parameter condition obtained by response surface method was as followed: rotational speed was 3 378 r/min, inlet velocity was 19 m/s, and number of rotor blades was 16. Under the control of these conditions, the cut size of turbo air classifier was 11.2 μm.