Abstract: Chemical demulsification treatment of waste oil-based drilling fluid was studied. The screened best demulsifier SA could recover the mineral oil and the oil recovery rate reached 93%. The optimal demulsification process parameters were determined: adding amount of demulsifier SA is 0.8%, PAC coagulant dosage is 600 mg/L, flocculants PAM dosage is 8 mg/L, and the reaction time is 1 h, temperature is (50±0.5)℃. Harmless treatment of isolated waste water and residue were also conducted.