We carry out float upward separation by making use of density difference of oil and water, that is, to deal with polluted water with oil by adopting physical separation method. As the polluted water goes to separator, first of all, it comes to one-level coarse graining coalescer, slowly pass through micropore of filter element, it is polypropylene fiber layer of outer layer of filter element, so that it can absorb oil globules, while inner layer is modified fiber layer, so that it can desorb oil globules, hence, it is essential to gather oil, forming to big oil globules, then rapidly float upward to oil drainage port. The left water goes to secondary coarse graining, then repeat the above separation course. The secondary pore diameter is shorter than the first-level one’s and density is larger than the first-level one’s, thereby, we can furthermore catch much smaller oil granules in water, to completely separate oil and water.