The technology is a kind of oil base drilling (completion) fluid developed for abnormally low pressure formations, strong water sensitive lithology, old areas with depleted formations, and complex oil and gas reservoirs. It can apply in the drilling construction of shale with an equivalent density of less than 1.00g/cm3 for abnormally low pressure formations and strong water sensitivity, and the construction of workover (completion) fluids with a minimum equivalent density of 0.60g/cm3 for old areas with depleted formations and special processes.