The planned depth of future continental scientific drilling program is 13000m, based on the geothermal gradient of 3℃/100m, the bottom hole temperature will reach more than 390℃, so the drilling fluids technology will face a severe challenge to be applied in an extremely high temperature and high pressure environment. In this case, the pilot study was carried out on the ultra high temperature drilling fluid, with salt resistant clay, high temperature filtration reducer, high temperature deflocculant and high temperature protective agent, the saturated salt water drilling fluid composition was developed, this drilling fluid could work in the environments of more than 230℃. The indoor evaluation test demonstrated that this drilling fluid can still keep good flowing property and the water loss is less than 35mL/30min after 230℃ rolling aging test for 16 hours.