Ammonium and silver co-doped phosphotungstic acid was prepared by ion-exchange method and used as catalyst for the synthesis of dioctyl adipate. The structure, acid strength and surface acid density of (NH4)0.5Ag0.5H2PW12O40 were characterized by FT-IR, XRD and Hammett indicator method. As shown by the results, (NH4)0.5Ag0.5H2PW12O40 performed the highest activity, and the esterification rate reached 99.8%. The catalytic activity of (NH4)0.5Ag0.5H2PW12O40 was higher than that of traditional single cation doped phosphotungstic acid. The catalytic property of (NH4)0.5Ag0.5H2PW12O40 for the synthesis of other dialkyl adipate was also investigated. And the esterification rate was over 99.5%. In addition, the esterification rate still reached up to 98.6% after (NH4)0.5Ag0.5H2PW12O40 recycling in 4 runs.