<p>Soil salinity is one of the main environmental limiting factors for plant growth and production. Sodium salt (NaCl) is the main salt in saline soils. The high-affinity K⁺ transporter (HKT1) is a Na⁺-preferential transporter identified in multiple glycophyte plants, and it participates in salt tolerance through shoot Na⁺ extrusion. However, there has been limited research on the identification and characterization of HKT1 from halophytes. In this study, SlHKT1.1 was cloned and functionally characterized from the halophytic shrub <i>Salix linearistipularis</i>. Sequence analysis revealed that SlHKT1.1 is a member of HKT1. Transient expression of SlHKT1.1 in tobacco leaves showed that it as a plasma membrane protein. Under NaCl and KCl stress, <i>SlHKT1.1</i> overexpression severely inhibited the root growth of transgenic poplar seedlings. Ion content measurements revealed significantly higher Na⁺ content in the roots of transgenic poplar seedlings than in wild-type roots. Correlation analysis showed that significant root growth inhibition was associated with higher Na⁺ accumulation in roots in transgenic poplar seedlings. Analyses of K⁺ content and flux rate revealed that SlHKT1.1 was not directly involved in the transport and accumulation of K⁺. These studies suggest that SlHKT1.1, a plasma membrane Na⁺-preferential transporter from <i>S. linearistipularis</i>, can be used for enhancing plant salt tolerance via tissue- or cell-specific expression.</p>