Metal ion and ammonium co-doped phosphotungstate were prepared and used as catalyst for the synthesis of tributyl citrate. Among them, (NH4)0.5Al2/3H0.5PW12O40 (I) showed relatively high catalytic activity and low cost. And the yield of tributyl citrate reached 97.1% with 4: 1 molar ratio of n-butanol to citric acid using 1.5% I as catalyst at 150oC in 3 h. The element composition, structure, surface acid strength and acid density of I were also characterized. The surface acid strength of I was in the range of -14.52 to -13.75, and the acid density of I reached 2.57 mmol/g, which was higher than that of traditional single cation doped phosphotungstate. In addition, the catalytic activity of I had no viewable change after 3 runs.