The difficulty of detecting genetically modified products lies in DNA extraction from deep-processing products.In this study,DNA from soybean lecithin which was chose as the research object,was extracted and purified by CTAB method,bead kit and NucleoSpin Food kit.The purified DNA was detected by real-time PCR using soybean lectin gene which was one of soybean endogenous genes.The detecting result showed that CTAB method was suitable for DNA extraction of soybean lecithin.By optimizing the conditions of CTAB method,improved Ⅱmethod was determined as the best DNA extraction method for soy lecithin.And DNA extracted by improved Ⅱmethod has high purity.The results of further testing of genetically modified ingredients confirmed that several commercial products were non-GMO.