Water, ethanol of 60%, 70%, 80%, 85%, 90%, 95% and 100% and methanol of 60%, 70%, 90%, 95% and 100% were used as solvent to test extracting rate of alkaloids from the fruit of black nightshade( Solanum nigrum L.). The result showed the ethanol of 80% had the highest extracting rate of alkaloids. Then, 80% ethanol was used as extraction solvent, different extraction temperature (20, 40, 60, 80, 100 ℃), extraction time (2, 3, 4, 5, 6, 7, 8 h) and ratio of material to solvent (1∶5, 1∶10, 1∶20, 1∶40, 1∶60, 1∶80, 1∶100) g/mL were designed to study the optimum extraction conditions of alkaloids. The results showed that: the best extraction solvent was 80% ethanol; optimum extraction conditions were 57.5 ℃ of extraction temperature, (1∶20.5) g/mL of material to solvent , 4 h of extraction time. On these conditions, the alkaloids extraction rate was (0.824±0.001) mg/g. By static adsorption and desorption testing of resins, the best resin was AB-8, the best purification conditions were 0.03 mg/mL of solution concentration, pH 9 of solution, 1∶10 of diameter to length, 3.0 BV, pH 3 and 70% ethanol with the elution flow rate of 2.0 BV / h, the alkaloid purity could increase 9.44 times.