Substituted diphenyl ethers (SDE) belong to an important fine chemical intermediates which can be synthesized via Williamson reactions. Room-temperature ionic liquid (RIL) as solvent could realize clean procedure of SDE′s synthesis. The authors prepared a RIL of 1-butyl-3-methyl imidazolium hexafluorophosphate (BMIMPF6), and synthesized a series of SDEs from substituted nitrobenze and phenol via Williamson reaction by use of BMIMPF6 as green solvent and K2CO3 as catalyst. Some factors affecting the etherification,such as temperature,time and catalysts etc,were studied,and the relatively optimal reaction conditions were worked out: molar ratio of reaction material/catalyst=1/1(molar),T=100 ℃,t=1 h. Under the above procedures the yield of resulting SDEs could be 70%-93%, and the structural confirmation was done by 1H NMR, 13C NMR and MS. One additional point should be emphasized that the RIL could be reused at least 5 times without noticeably deteriorating SDE′s yield and purity. This is beneficial to environmental protection.