To use solid immersion lens is one of the practical methods to realize the near-field high-density optical data storage. But the storage system will work only on the condition that the distance between the bottom of the SIL and the surface of media is exactly controlled within the sub-wavelength scale. In this letter the flying height of the SIL is measured by the capacity between the SIL and the disc, and the SIL fixed in flying head is loaded on the surface of the rotating disc by flexible cantalever. The SIL will fly at different height with the different rotating speed of the disc. When it works, a computer is used to detect the flying height of the SIL, and after comparing this result with the preset value, it controls the disc to accelerate or decelerate, and this will result in adjusting the flying height of the SIL. In this way a certain height within the scale of 150~600 nm of the flying height over the disc surface is dynamically controlled when the disc is rotating in high speed.