Abstract: When pretreating mixed Fengcheng super heavy crude oil (containing 60—70% Fengcheng super heavy crude), overload of electric current often happened at the electric desalting device of delayed coking unit. It was found that processing crude with high water content from the bottom of crude tank was the main reason. In order to keep electric desalting unit running safely and smoothly, some improvements were conducted, such as increase the dewater frequency and temperature of crude tank, mixed processing the high water bottom crude in small amount with conventional crude, shifting the demulsifier injection spot forward, decrease the mixing force of mixing valve, as well as the transformer voltage. Since then the water and salt contents of purified crude dropped to less than 0.5% and 7.5 mgNaCl/g, respectively. Some other measures to further reduce the water and salt contents of Fengcheng crude for meeting the required targets (less than 0.3% and 3.0 mgNaCl/g, respectively) were proposed as well.