The demulsification of high paraffinic content crude oil from the South Sea were explored by 3 kinds of different molecule weight nitrogenous polyether demulsifiers (PRO7501X,X=A,B or C) with a traditional bottle test. The influences of types, concentration and molecule weight of the demulsifiers on demulsification properties were discussed in detail. Through on-site pilot and dosing point transformation, the actual dehydrated water purification ability of demulsifier PRO7501B in the scene actual was investigated. Experimental results show that PRO7501X performed higher interface activity than the field usage demulsifier under the action of 10 min. In the experimental range, the demulsification ability was closely related to the molecule weight of demulsifier. The Dehydration rate was improved with the increase of demulsifiers concentration, and tends to be stable at the demulsifiers concentration of 15 mg/L. After the onsite pilot, PRO7501B can decrease the water percent in oil of separator PV103 from the initial 11.0%~15% to 0.2%~1.0% and decrease the oil content in water phase from 30~35 mg/L to below 3 mg/L, which can basically resolve the problem of the oil film in the sea.