A class of compounds of monosulfonic phenyltetrazole, with the structure of 2-(R1 phenyl)-5 (2-sulfonic phenyl)-2H-tetrazole. The 2-sulfonic phenyl tetrazolium salt of this invention has advantages of low toxicity, short synthetic route, easy control of purity and quality. As the 2-sulfonic phenyl tetrazolium salts has almost no absorption at 450 nm where the reduzate has greater absorption, spectrophotometry can simply and rapidly determine the activity of glutamate dehydrogenase, or the content of NADH/NADPH.