During the production of Gaotan-1 well in Junggar Basin，a large amount of black solid-like sediments were formed on the inner wall of oil tubing，which seriously affected the production. Aiming at this problem，trichloroethylene was used to extract organic and inorganic substances from different parts of the sediment in wellbore. The composition of organic and inorganic substances was characterized. At the same time，the influence of inorganic substance on the adsorption and deposition of crude oil was analyzed，then the formation mechanism of sediment was further explored. The results showed that the content of organic and inorganic components was quite different. The inorganic content in the center of the sediment reached 71.51%，but that was only 16.55% in the darker part of the surface. However，the content of organic compounds in different parts was similar，with asphaltene accounting for 52.71%—58.37%. The asphalt molecular connected with large side chain length and a high degree of branching was more likely to be deposited. The inorganic substance in the sediment was mainly barium sulfate. Its lamellar structure with rough surface intensified the adsorption of asphaltene. The deposition mechanism of asphalt scale in Gaotan-1 well was that inorganic particle such as lamellar barium sulfate with 1—20 μm adsorbed the association of asphalt molecule with long side chain and high branching degree in crude oil，then the large particle accumulation with 20—100 μm was aggregated，which together formed deposit and adhered to the wellbore，resulting in the blockage of pipe string.