The invention relates to a molecular sieve sorbent, in particular to a flue gas desulphurization sorbent applicable to the treatment of SO2 in boiler flue gas. The sorbent comprises the following compositions by mass percentage: 0.1 to 5 percent of V2O5, 4 to 30 percent of CuO and 65 to 95.9 percent of silicon-aluminum molecular sieve. The molecular sieve sorbent takes molecular sieve as a carrier and contains vanadium and copper at the same time; moreover, a small amount of boron, aluminum, magnesium, titanium, chromium, manganese, iron, cobalt, nickel, zinc, zirconium, molybdenum, argentum, platinum, rhenium, or one or more elements in lanthanide or corresponding oxides can be added in the molecular sieve sorbent. The sorbent has the advantages of high adsorption capacity, excellent reproducing property, long service life and the like, and is not only applicable to flue gas desulphurization, but also applicable in gas purification fields such as CO removal and nitrogen oxide reduction.