The invention discloses a method for synthesizing 8th-site substituted-3,4,7,8-tetrahydro-2H-oxocin-2-one octatomic ring. The synthesis method includes the following steps: performing Grignard reaction on an aldehyde or ketone to obtain an allyl alcohol compound; and performing condensation reaction with 2-(tert-butylsulfonyl)acetic acid to obtain an allyl (tert-butylsulfonyl)acetate compound; performing olefin cross-metathesis reaction under the action of a second generation Grubbs catalyst to obtain a methoxycarbonyl (tert-butylsulfonyl)acetate compound; performing intramolecular reaction byusing anhydrous N,N-dimethylformamide as a solvent in the presence of a catalyst palladium acetate and a ligand triphenylphosphine, so as to produce a 3-tert-butylsulfonyl 8th-site substituted-3,4,7,8-tetrahydro-2H-oxocin-2-one octatomic ring lactone compound; and finally removing tert-butylsulfonyl in a reaction solution of sodium amalgam and acetic acid by taking ethanol as a solvent, so as toobtain 8th-site substituted-3,4,7,8-tetrahydro-2H-oxocin-2-one octatomic ring lactone compound. The yield of the method is high, and a solution with a very dilute reaction concentration is not neededin the synthesis of various substituted octatomic ring lactones through intramolecular catalysis by palladium, so the process conditions are simple and universal.