The invention provides a drill bit of a tree planting and digging machine. The drill bit comprises a knife rod, a spiral soil feeding knife and a spiral soil cutting knife, wherein the spiral soil cutting knife is of an inverted cone shape, has a blade outside a spiral knife and has an inner cone hole in the middle; a lower half of the spiral soil feeding knife is also of the inverted cone shape and is welded in the inner cone hole of the spiral soil cutting knife; a linear hole for accommodating the knife rod is formed in the middle of the spiral soil feeding knife; and the spiral soil feeding knife is welded on the knife rod by a welding process.