Abstract: The magnesium protoporphyrin IX methyltransferase （ChlM） is one of the key rate-limiting enzymes in chlorophyll synthesis and development of chloroplasts, which plays an important role in plant growth and development. To better understand the role of ChlM in Cymbidium goeringii, ChlM gene was cloned from the tissue culture seedling of Cymbidium goeringii ‘Song Mei’. The full-length open reading frame of ClChlM1 was 945 bp and encoded 314 amino acids. The sequence alignment showed that ClChlM1 contained an Mg-por_mtran_C domain, and subcellular location analysis indicated ClChlM1 was located in chloroplast. Furthermore, the overexpression of ClChlM1 in tobacco leaves could significantly increase the content of chlorophyll and ALA compared with wild type tobacco leaves. In addition, the leaf area of overexpressed tobacco was larger than that of wild type. In the over-expressed transgenic lines, the gene expression of glutamate -1- semialdehyde 2,1- aminomutase （Gsa）, chlorophyll a/b binding protein （LHCB）, magnesium chelatase CHLI and magnesium chelatase CHLH were up-regulated.