Objective To establish a simple,accurate and practi cal method of extracting plasmid from gram-negative and gram-positive bacteria ,Method we selected,Biswajit sahas method and comported others method, such as controlling pH andtemperature strictly and increasing EDTA-Na2 capacity． Result The eight strip s of Ecliv 5l7 can not be found completely in original method, but can be found in our one．We found the largest plasmid molecular weight was l86.3?kb, and t he minimum was l.l?kb from each 30 strains STA, EC, PA． Plasmid profile is alike through repeating ex p eriment three times． Conclusion:The method can be widely used in extracting bac teria plasmid and fit gram-negative and gram-positive bacteria whenever molecular weight ma x or min． These conditions can be obtained in general laboratory．