Abstract: The article aims at the reservoir damage problem of the drilling operation of HPHT gas-condensate well.Based on analysis of the newest design method at home and abroad,laboratory test and software simulation,a new design method of underbalanced drilling had been put forward.The method analyzed such factors as well control safety,borehole stability,oil locking damage of condensate gas reservoir of retrograde condensate and water locking damage due to capillary suction comprehensively,at the same time,it considered the effects of temperature and pressure on drilling fluid density and viscosity in hydraulic parameter calculation.In order to ensure bottom hole pressure in underbalanced condition in the whole process of drilling,tripping and making a connection,matching RBOP and DDV were installed,technical measures optimized.Design analysis was conducted in detail,taking Well B-0008 in B Block of Saudi as example,the design method could not only ensure downhole safety,but also could avoid reservoir damage,improving the success rate of oil and gas discovery in exploration wells.