We have determined the selenium(ⅳ) according that when pH1.0~ 3.0. and the non-ionic surface active agent OP-10 existence Se(ⅳ) with H_2NCSNH_2 can produce complex compound whose complexing ratio is 1: 2, and who is stable. 此方法利用了Se(Ⅳ)与硫脲H2NCSNH2在pH1.0~3.0的介质中,并有非离子表面活性剂OP-10存在时能生成络合比为1:2的稳定黄色络合物的原理来测定硒。