The production process of traditional polyether demulsifiers using ethylene oxide and propylene oxide as raw materials is dangerous and complicated，and the demulsification performance is still difficult to satisfy the requirements of actual production. In this paper，an ionic liquid demulsifier BADT-IL for the dehydration of W/O emulsion was synthesized using waste PET plastic as raw material. The chemical structure of BADT-IL was analyzed by Fourier transform infrared spectroscopy（FT-IR）and nuclear magnetic resonance hydrogen spectroscopy （¹H-NMR）， and the effects of BADT-IL concentration， sedimentation time， demulsification temperature，salinity and pH value on the demulsification efficiency of crude oil emulsion were investigated in detail. The demulsification mechanism of BADT-IL in crude oil emulsions was investigated through various methods including the measurements of the interfacial tension （IFT），zeta potential，contact angle （CA），coalescence time，and microscopic observation. The study revealed that the addition of 250 mg/L of BADT-IL to crude oil emulsions containing 70% water content resulted in a demulsification efficiency of 95.23% after static settling at the temperature of 60 ℃ for 180 minutes. Under similar conditions，demulsification efficiency reached 99.22% in crude oil emulsions with 30% water content，producing a clear separated water phase with a clean oil-water interface. BADT-IL demonstrated strong resistance to salt，with the increase of salinity，the demulsification efficiency improved. At a salinity of 50 g/L，the demulsification efficiency of crude oil emulsions with 70% water content reached up to 96.33% . As the demulsification temperature rose，both the demulsification rate and efficiency increased significantly. Compared to typical commercial demulsifiers， BADT-IL exhibited exceptional demulsification performance. BADT-IL could effectively reduce IFT at the oil-water interface during demulsification，replace the emulsifier at the interface，form an unstable composite interfacial film，facilitate droplet coalescence，and consequently ensures efficient oil-water separation.