Polyethylene glycol(PEG) membranes with different molecular mass cut-offs were used to treat oil/water emulsion, and the effects of experimental conditions including pressure, temperature and different opera-ting modes on permeate flux and removal rate of chemical oxygen demand (CODCr) were studied. The results show that the permeate flux of ultrafiltration membrane is influenced by pressure and temperature; practical pressure is chosen to be 0.3-0.7 MPa for the PEG with molecular mass cut-offs of 8 000 and 0.7-1.0 MPa for the PEG with molecular mass cut-offs of 2 500; and the practical temperature is chosen to be 25-32 ℃. Different operating modes of ultrafiltration also influence the permeate flux and removal rate of CODCr. The ultrafiltration membrane of intermittent cross-flow operating mode is easier to be influenced by blocky polarization and contamination than that of sequential cross-flow operating mode. Removal rate of CODCr in intermittent cross-flow and sequential cross-flow condition can be maintained at about 93%.