Abstract: Urea as an important fertilizer and the non-protein-nitrogen can be faster de-composed into ammonia and carbon dioxide in the presence of urease,In order to control the decomposition rate,the inorganic compound was selected as an inhibitor,which was capable of proloning urea decomposition when added some urease to the reactive system.Under the exist of this inhibitor in the urease,the urea decomposition rate was determined by using NH_3 -gas selective electrode.It was found that the inhibitor can significantly inhibit the urease ac-tivity.The inhibition mechanism was also studied.