Abstract: The selection of the velocity ratios for air jet vortex generator is considered. The concept of the optimum velocity ratio with the maximum vortex induced velocity at the wall,Ropt·v ,and the concept of the optimum velocity ratio maximizingshape factor of boundary layer ,Ropt·H, are introduced.Based on the empiricalrelationships summarized from the measured data of the side-inclined jet/ crossflow interaction flow field, the formulas forRopt·v may be deduced as follows Ropt·v = 3.22(X/D + 0.3019)-0.219 R≤1.8Ropt·v = 2.75(X/D + 0.3019)-0.111 R≥1.8The predicted values of Ropt.Hare determined according to the experimental results of the reverse flow region behind the jet hole in association with the Ropt·v empirical formulas. They agree with the measurements of the boundary layer at the flate plate.