We present a non optical shear force detection system for tip sample distant control in scanning near field optical microscopes.When the vibrating tip is damped by the shear force

the voltage of the tip is decreased.Detecting this decrement tip sample distance can be easily controlled.Using the method

we can easily put the tip into the working area and keep the apposite height while the tip is scanning.We measure the curve of the frequency dependence of the induced voltage on the tip system and the curve of shear force signal versus tip sample distance.We demonstrate the performance of our distance control on a surface of a CD with the scanning range 4μm×4μm.