Abstract: In this study, we isolated six members of the CA family of genes, namely PsnCA1,PsnCA2,PsnCA3,PsnCA4,PsnCA5 and PsnCA6 respectively in Populus simonii×P. nigra.Of which PsnCA4 and PsnCA6 belonged to the family of α carbonic anhydrase,and PsnCA1,PsnCA3 and PsnCA5 belonged to the family of β carbonic anhydrase,and PsnCA2 belonged to LbeatH super gene family. The results of phylogenetic classification showed that PsnCA1, PsnCA3 and PsnCA5 were clustered into one category, while PsnCA2, PsnCA4 and PsnCA6 belonged to another category. Real-time PCR was used to investigate the PsnCA gene expression pattern in roots, stems and leaves, and the results shows: except PsnCA6, the remaining five gene expression levels in the leaves were significantly higher than the roots and stems. The highest expression in the leaves was PsnCA1, and the highest expression in the stems and roots was PsnCA3. PsnCA expression governed by the dark treatment in various tissues, the largest gene expression changed in roots,followed by the stems and leaves.