With the continuous development of oil/gas drilling to the deep，the temperature of deep and ultra-deep formations drilled are getting higher and higher，which puts forward more requirements for drilling technology，especially technology of drilling fluid. In combination with the actual requirements of ultra-high temperature drilling，the technical barriers of water-based drilling fluid under ultra-high temperature and the effect of ultra-high temperature on water-based drilling fluid performance were analyzed. Research progress of key additives for water-based drilling fluid under ultra-high temperature and water-based drilling fluid system they constructed was described，and the future development direction of water-based drilling fluid under ultra-high temperature was discussed.