In view of the deficiency of environmental protection and application performance of weighting agent including barite， iron ore powder，ilmenite powder and calcium carbonate，the double-protection weighting agent was obtained by optimizing calcium carbonate weighting agent calcite，and compounded barite and calcite in mass ratio 7∶3. The performance of double protection weighting agent was optimized by particle size matching，dry activation treatment and surface coating modification. The compatibility of double-protection weighting agent with four kinds of drilling fluids and its protective effect on oil and gas reservoir were studied. It was applied on 10 wells in Dagang oilfield to evaluate its impact on the environment. The results showed that the double-protection weighting agent reduced the influence on the viscosity of drilling fluid，had good compatibility with drilling fluid，solved the problem of arsenic exceeding the standard requirements and had a good protection effect on oil and gas reservoir. The core permeability recovery value could be increased by 15.2 percentage points compared with that of barite. Field application results showed that the drilling of implementation wells was carried out safely. Compared with the average value of adjacent wells， the rate of penetration was increased by 49.18%，the average diameter expansion rate was reduced by 1.84 percentage points，and the single well in average had an oil increase of 0.60 t per meter in production zone. The heavy metal arsenic content of filter cake was less than 60 mg/kg，which met the requirements of national standard.