Abstract: Well Tashen-1 is an ultra-deep scientific exploratory well,with its designed depth being 8000m and completed depth 8408m,and its target formation in the Cambrian system.Accidents,such as leakage of drilling fluid,collapse,enlargement of the hole diameter,jamming of the drilling tool,easily occur during drilling the well due to its location in complex strata.In order to improve the solid carrying capacity of drilling fluid of ultra-deep wells,drilling fluid types are selected based on different times of spud drilling.CMC-HV bentonite drilling fluid is used in the first spud drilling to protect the well head.Low solids polymer drilling fluid is used in the second spud drilling to ensure large displacement,low shear viscosity,strong encapsulation,and on-time short trip in definite drilling footage,so as to effectively avoid tool sticking.The polymer sulfonated anti-collapse drilling fluid is used in the third spud section of the well,which helps strengthen the inhibition of the drilling fluid system,avoid wellbore collapse,and improve the temperature-and salt-resistant capacities of drilling fluid.The sulphonic polymer drilling fluid technology with shielding and high temperature resistant properties is applied to the fourth and fifth spud section and helps tackle the technical problems of high temperature,high pressure,collapse,sticking,bad leakage,solid invasion,gypsum-salt pollution,and annular sand-carrying,providing good experience for drilling and completing ultra-deep wells.