Ultra high vacuum - field ion microscopy (UHV-FIM) with atomic resolution was used to study the methods of preparing ultra-sharp single atom tips. Several treatments including annealing, depositing, exposing to special gas, keep in a given atmosphere, and so on were the possible tactics to sharpen the tips. The sharpen results of various treatments were observed by field ion microscope. Two kinds of magnetic nano tips were formed. One is a PtCo pyramidal tip formed by surface faceting, the other is a Pt based Co tip formed by the SK mode epitaxy.