Abstract: According to the experiment research on settling character of crude oil, the settlement process is divided into chaotic period, temporary-stable period, coagulation period and stable period. The settlement regularity including colloidal particle coagulation and destabilizing dehydration of emulsion in the crude oil storage process is studied. Through analysis of oil sludge composition, generating amount of oil sludge and relations between it and crude oil character, the elementary stacked mechanism of oil sludge is obtained.