Dtype cyclin (CYCD) regulates the G1/S phase transition of the cell cycle. CYCD combines with CyclinDependent Kinase (CDK) to form CYCD/CDK complex. The activated CYCD/CDK complex regulates the cell cycle through phosphorylation of downstream cell cycle response factors, which in turn affects plant growth and development. In this study, ‘741 poplar’ was used as experimental material, and a D2type cyclin gene was identified(PtoCYCD2; 1). The results showed that: (1) Quantitative real time polymerase chain reaction (qRTPCR) showed that PtoCYCD2; 1 gene was expressed in roots, stems, leaves, petioles, bark, and xylem, with the highest relative expression in leaves. (2) Subcellular localization indicated that PtoCYCD2; 1 protein was localized in the nucleus. (3) Compared with the wildtype poplar (WT), ‘741 poplar’ overexpressing PtoCYCD2; 1 gene showed reduced plant height, reduced stem diameter, and significantly lower leaf volume. (4) Scanning Electron Microscope (SEM) analysis showed that cells of transgenic poplars were smaller and more numerous than those of WT. Resin section showed that, compared with WT, the intercellular space of the fence tissue and sponge tissue of the transgenic poplar leaves was loose. (5) qRTPCR showed that, overexpressing PtoCYCD2; 1 gene in ‘741 poplar’, the expression levels of CDKA; 1, CDKB1; 1 and CDKB2; 1 were significantly upregulated, while retinoblastomarelated protein1 (RBR1) gene, cyclindependent kiprelated protein (KRP) gene expression level were significantly downregulated. This study lays a foundation for further understanding the function of CYCD2 gene in woody plants.