Abstract: Poa pratensis is a typical rhizome grass, of which rhizome is an important organ for nutrient storage and vegetative reproduction that plays an important role in improving plant surface invasion and underground soil consolidation. The occurrence and development of rhizomes are closely related to endogenous hormones. This study investigated the hormone regulation mechanism of rhizome expansion by examining the correlation between the rhizome expansion ability and endogenous hormones contents in nine ecotypes of wild P. pratensis from different areas of Gansu Province and 'Midnight Ⅱ' P. pratensis (the control). The purpose of this study was to provide a theoretical and practical basis for new variety breeding and lawn maintenance and management of P. pratensis. The results indicated that: 1) there were differences in the rhizome expansion ability among the wild P. pratensis ecotypes. P. pratensis from Yuzhong had the largest tiller number, rhizome number, aboveground biomass, and stem node length, whereas P. pratensis from Xihe had the largest coverage area, longest rhizome, and highest rhizome biomass. The rhizome expansion ability of P. pratensis from strong to weak was P. pratensis from Yuzhong > from Xihe > from 'Midnight Ⅱ' > from Weiyuan > from Lingtai > from Qingshui > from Sunan > from Qinzhou > from Xiahe > from Anding. 2) The distribution of endogenous hormones in the rhizome and stem base of P. pratensis was significantly different; the gibberellic acid (GA₃), indole-3-acetic acid (IAA), and abscisic acid (ABA) contents were rhizome > stem base; the zeatin (ZT) content was stem base > rhizome; and the GA₃ content in the two parts was significantly higher than that of the other hormones. 3) Correlation analysis showed that the rhizome expansion ability of P. pratensis was positively correlated with the ZT content, stem base ZT/ABA, and IAA/ABA (P < 0.05) but negatively correlated with rhizome GA₃/IAA (P < 0.05). However, there were no correlations between the IAA, GA₃, and ABA contents. In summary, P. pratensis from Yuzhong, which has better rhizome expansion ability than 'Midnight Ⅱ', is good for variety breeding; the higher ZT content and ratio of IAA/ABA to ZT/ABA and the lower GA₃/IAA ratio are beneficial to the rhizome expansion.