NOVELTY - Processing oil field sewage and fixing carbon dioxide biodiesel using micoalgae comprises e.g. using cavitation air floatation for oil field sewage combined station of oil field sewage for biological degreasing pretreatment, adding crude oil oilfield wastewater in aerobic biological treatment system to remove crude oil, degreasing, adding nitrogen, phosphorus nutrients in aerobic biological degreasing process, directly flowing oil field sewage into track type algal culture system, passing flue gas, adding microalgae species, growing, conveying oilfield wastewater into ultra-filtration system.    USE - The method is useful for processing oil field sewage and fixing carbon dioxide biodiesel using micoalgae (claimed).    DETAILED DESCRIPTION - Processing oil field sewage and fixing carbon dioxide biodiesel using micoalgae comprises (a) using cavitation air flotation (CAF) for oil field sewage combined station of oil field sewage for biological degreasing pretreatment, adding air floatation removed crude oil oilfield wastewater in aerobic biological treatment system for removing crude oil and degreasing, adding nitrogen and phosphorous nutrient in aerobic biological degreasing process, after the aerobic biological treatment, oilfield wastewater contains crude oil less than 2mg/l, (b) directly flowing resulting oilfield sewage into track type algal culture system, then passing flue gas with carbon dioxide content of 3-15%, adding microalgae species in track type micro-algae culture system, growing for 5-15 days, when oilfield sewage medium density is 107/ml or more, fat containing rate is more than 20%, and (c) conveying processed oilfield wastewater into ultra-filtration system, using ultra-filtration membrane, cross-flowing sewage through ultra-filtration system and collecting microalgae, pressure filtering algal slurry by filter to obtain algal cake, which is conveyed to bio-diesel process, sterilizing ulra-filtration production clean water, deoxidizing, reinjecting into low-permeability or ultra-low permeability oil reservoir stratum for oil displacement.