An oil mist filter is fixed on an air intake of an oil mist collector and contains: a first cover, a second cover, a first filtering unit, a third cover, and a second filtering unit. The first cover is hollow and includes a first through orifice. The second cover is hollow and includes a second through orifice. The first filtering unit is fixed between the first cover and the second cover and includes a chamber for guiding oily substances from the first through orifice. The third cover is placed in the chamber and includes a collection portion and plural arcuate guiding portions radially extending outward from the collection portion. The second filtering unit is disposed between the second cover and the third cover to filter the oily substances from the chamber, and then the oily substances are guided out of the second through orifice via the plural guiding portions.