Abstract: The relationship of surface active site and turnover frequency versus activity for ammonia synthesis catalyst which were obtained from different iron oxide as precursor were investigated by means of a physisorption of N 2 and a chemisorption of CO and CO 2 and activity test.The exposure percent of active iron atom on the surface was lower than one percent, which indicates that more than 99% of the iron atom were buried in the internal of catalyst.The change of activity,specific rate,turnover frequency,acid coverage and the coverage ratio of acidic to alkalic surface area had a similar regularity with the change of the state and the composition of iron oxide precursor of catalyst. With increased FeO content,the surface properties and surface structure of the reduced catalyst were changed,and the number of active site was decreased and the intensity (TOF) of active site was increased.FeO might be advantageous to the formation of FeAl 2O 4 iron aluminate in the presence of Al 2O 3,and surface restracturing of FeAl 2O 4 to iron crystal face increased the activity of catalyst.