A new method for nanometer positioning based on surface plasma wave is reported. A fiber probe approaching a coated prism can be equivalent to a four-layer prism-metal-air-fiber system. Analysis of the near-field beam intensity entering the fiber probe is presented. Theoretical analysis shows that the intensity coupling into the fibre probe changes according to the thickness of air gap. Non-contact nanometer indicating system can be set up according to this characteristic. Experiments show that standard deviation of 2 nm and resolution of 0.1 nm/nV in 20 minutes procedure of positioning repeatability can be achieved under air conditioning of ±1℃/h.