Abstract: Conventional high-density oil based drilling fluids are not effective in enhancing ROP. Further, their rheological properties cannot be controlled easily. By means of creating a new molecular structural design, the high temperature resistant emulsifier, HT-MUL, and the rheology modifier, ZNTQ-I, were developed. In addition, the high temperature resistant high-density clay-free diesel oil based drilling fluid was prepared. Performances of the emulsifier and rheology modifier were individually evaluated through electric stability tests and aging tests under high temperature. The clay-free diesel oil-based drilling fluid developed was tested for its temperature resistance, stability, anti-pollution and inhibitive properties. Test results demonstrate that HT-MUL has a high emulsion-breaking voltage and temperature resistance up to 220 degrees, and a clear rheological increase is obtained for ZNTQ-I when its concentration is 0.5%. In addition, the newly-developed drilling fluid possesses an emulsion-breaking voltage of approximately 2 000 V with allowable tolerance to pollution of distilled water with mass fraction of 25% and pollution of CaCl2 solution with mass fraction of 15% under 2.50 kg/L and at the temperature of 150-220 degrees. Results indicate that the newly developed drilling fluid has a density up to 2.50 kg/L and temperature resistance to 220 degrees. With satisfactory stability, suspension capacities and anti-pollution capabilities, the drilling fluids can help to enhance ROP and protect pay zones.