The invention relates to a selective blocking method of a horizontal well reservoir. Through screening, a certain interval, which is already perforated or subjected to reservoir modification, of a horizontal well is regarded as a target interval of blocking construction; shafts in a range of 30 m above a top boundary of the target interval subjected to blocking construction and shafts in a range of 30 m below a bottom boundary of the target interval subjected to blocking construction are treated, and burr, scaling substances, sand and greasy dirt which affect the subsequent construction quality are eliminated; a bridge plug setting pipe column is tripped in, a bridge plug is set 15 m below the bottom boundary of the construction target interval; a cement retainer setting pipe column is tripped in, and a cement retainer is set 15 m above the top boundary of the construction target interval; a cement retainer back-insertion pipe column is tripped in, and back-insertion motion of the cement retainer is completed; according to designed examining seal displacement, a tubing or coiled tubing positive cycle pump is used for injecting clear water to conduct cement retainer examining seal;according to designed blocking construction displacement and designed cement slurry volume, reservoir blocking is conducted. Effective squeezing blocking and under-pressure wait on cement can be achieved, construction accident risks in conventional squeezing blocking work can be avoided, and the effect and the efficiency of horizontal well reservoir blocking are greatly improved.