Poly[4,4'-(diphenyl ether)-5,5'-bibenzimidazole] (oPBI) based high temperature proton exchange membranes are prepared by covalent cross-linking with chloromethylated polysulfone (CMPSU) and doping with zirconium phytate (ZrPA). ZrPA is synthesized as the proton conductor through a facile method from zirconyl chloride and phytic acid which is abundant and readily available. oPBI is cross-linked by CMPSU and that hydrogen bonds are formed between ZrPA and oPBI-CMPSU. The composite membranes are dense without through holes when doping with ZrPA. The composite membranes exhibit good thermal stability below 140 degrees C. Meanwhile, the composite membranes reveal good mechanical strength and methanol resistance. The oxidative stability is improved because of cross-linking and the doping of ZrPA. Conductivities of oPBI-CMPSU/ZrPA at different temperatures and relative humidity (RH) are investigated. At 100% RH, 50% RH and 0 RH, the conductivity of oPBI-CMPSU(20%)/ZrPA(30%) can reach 0.072 S/cm, 0.025 S/cm and 0.012 S/cm at 140 degrees C, respectively. Although the proton conductivity of the composite membrane was not particularly high at 100% RH, the composite membrane comparatively exhibited good proton conductivity at high temperature and at 50% RH and 0 RH.