Abstract: DNA bar code, a special DNA sequence used in species identification, has become a focus in biological taxonomy research in recent years. It has been wide applied in zoological taxonomy. And the used DNA sequence was the partial sequence of mitochondrial cytochrome C oxidase gene No. I （CO I ）.The progress of DNA bar code is relatively slow in botanical taxonomy. The proposed fragments of chloroplast DNA including rpoB, rpoC1, mark and rbcL were compared and evaluated at present. The paper illustrates present application, existing problems and possible tendency of DNA bar code in biological taxonomy.