To provide immersive freehand painting experience, we proposed a flexible airbrush model making use of the hands tracking capability of Leap Motion Controller. The airbrush model uses a common screen as the painting canvas. When the user moves hands over the screen, the brush model continually acquires his/her hands movement data and extracts multiple control signals which describes multiple gestures. The virtual airbrush moves along with the user's hands movement as if it is fixed on his/her finger, and its properties change with gestures' change. When the virtual airbrush intersects with the screen, it continually exerts paints onto the screen. User test shows that the user can easily create multifarious brush stroke effects by directly operating over the screen.