Chemical demulsification method is effective for treating waste oil base drilling fluid，but the lack of special demulsifier has limited its application in the field. In this paper，a special waste oil-based drilling fluid demulsifier，named as ZYFYP，which consistd of AE8051，BP-169，AP-05 and OP-10，had been developed. The effect of ZYFYP in treating waste oil-based drilling fluid of Jiao-51 Well was remarkable during demulsification-flocculation-separation treatment process. Under the condition of ZYFYP amount of 0.8%（mass ratio of AE8051，BP-169，AP-05，OP-10 of 3:2:1:3），flocculant agent PAM amount of 0.2%，surfactant OT-15 amount of 1.2%，dispersant Na₅P₃O₁₀ amount of 10%，the oil recovery rate was 98.6% after centrifuge separation for 5 minitues at the speed of 3500 r/min and at the temperature of 15—50℃. ZYFYP was suitable for treating different density waste oil-based drilling fluid in solid-liquid separation process. Heating process was not needed，equipment requirement was not high and the cost was low，the oil recovery rate from waste oil-based drilling fluid was greater than 96%.