The major application of the scanning tunneling microscope (STM) is as a local surface topography and structure probe. The scanning tip usually is made of metal such as tungsten (W), platinum-iridium (Pt-Ir), gold (Au), etc., by electrochemical etching or mechanical cutting. STM has also recently demonstrated its potential application as a powerful tool for nanometer-scale surface modification. We made a kind of diamond STM tips by the MPCVD technique. The tips are quite stable, and hard enough to polish the metal film surface to produce relatively flat areas. Both SEM and STM were employed to check and analyze the tips and the results of polishing.