NOVELTY - Hydrochloric acid and nitric acid are mixed, 2 portions of solar cell are placed in mixed solution, and silver grid line on solar cell is removed. The surface of solar cell is cleaned, and placed in hydrofluoric acid, to form silicon nitride film. The solar cell is washed with water, and conductivity is measured. When the conduction is P-type, the reaction is stopped, to form silicon substrate of solar cell. The resistance and carrier lifetime of obtained solar cell silicon substrate are measured. Thus, the quality of solar cell silicon substrate is tested.    USE - Quality testing method of solar cell silicon substrate.    ADVANTAGE - The method economically provides solar cell silicon substrate having high quality and reliability, by a simple process.    DETAILED DESCRIPTION - An electrical performance of solar cell is recorded. Hydrochloric acid and nitric acid are mixed in a ratio of 10-1:1-20, to obtain mixed solution. Two portions of solar cell are placed in mixed solution, and silver grid line on 2 sides of solar cell is removed. The back surface of solar cell is cleaned, and placed in hydrofluoric acid solution. The solar cell is removed, and silicon nitride film is formed. The film-formed solar cell is washed with pure water for 1-3 minutes, and conductivity is measured on both sides of film. When the conduction is N-type, the reaction of solar cell is continued. When the conduction is P-type, the reaction is stopped, to form silicon substrate of solar cell. The solar cell is removed, washed with pure water and dried. The resistance of obtained solar cell silicon substrate is measured using four-point probe, and minority carrier lifetime tester is used to measure minority carrier lifetime. The electrical performance and other data are compared with normal solar cell. The normal solar cell has resistivity of 1 Omega .cm. The average minority carrier lifetime of normal silicon substrate is 1 mu second. The average minority carrier lifetime of obtained silicon substrate is 1.4 mu seconds greater than that of normal silicon substrate. The content of analytically pure hydrochloric acid and analytically pure nitric acid is 36-38%, and 68-70%, respectively. The volume of mixed solution containing nitric acid, hydrochloric acid and hydrofluoric acid is 1-20%. The concentration of hydrofluoric acid is 20% or less. Thus, the quality of solar cell silicon substrate is tested.