The invention relates to a hypofluorescence film forming filtrate reducer and a preparation method thereof, which belong to the technical field of chemical engineering additive for oil drilling. The hypofluorescence film forming filtrate reducer is prepared from cotton cake powder, olefin, 1 percent of aqueous sodium hydroxide solution and span 80. The filtrate reducer has a simple production process, low manufacturing cost, good capacity for high-temperature resistance and salt resistance, hypofluorescence, nontoxicity, small filtration loss amount and good lubricating performance, can meetthe requirement of environmental protection, effectively reduces the dynamic filtration loss amount and dynamic filtration velocity, is favorable for the stability of well wall, improves oil extraction rate of perforation, prevents a drilling fluid and a filtrate from penetrating into a mud shale body, effectively prevents stratum from hydrating, expanding and collapsing, is smooth to pull out and run into holes, prevents blocking and clamping, and solves the problems that the prior filtrate reducer uses mass macromolecular materials, has high price and a complex production process, produces mass substances polluting environment, has poor capacity for resisting high temperature, salt and drill chip contamination and is not favorable for the stability of the well wall. The hypofluorescencefilm forming filtrate reducer can be used for a straight drilling well, an inclined well and a horizontal well.