BackgroundMedicago sativais the most important forage world widely, and is characterized by high quality and large biomass. While abiotic factors such as salt stress can negatively impact the growth and productivity of alfalfa. Maintaining Na+/K+homeostasis in the cytoplasm helps reduce cell damage and nutritional deprivation, which increases a salt-tolerance of plant. Teosinte Branched1/ Cycloidea/ Proliferating cell factors (TCP) family genes, a group of plant-specific transcription factors (TFs), involved in regulating plant growth and development and abiotic stresses. Recent studies have shown TCPs control the Na+/K+concentration of plants during salt stress. In order to improve alfalfa salt tolerance, it is important to identify alfalfaTCPgenes and investigate if and how they regulate alfalfa Na+/K+homeostasis.ResultsSeventy-oneMsTCPsincluding 23 non-redundantTCPgenes were identified in the database of alfalfa genome (C.V XinJiangDaYe), they were classified into class I PCF (37 members) and class II: CIN (28 members) and CYC/TB1 (9 members). Their distribution on chromosome were unequally.MsTCPsbelonging to PCF were expressed specifically in different organs without regularity, which belonging to CIN class were mainly expressed in mature leaves.MsTCPsbelongs to CYC/TB1 clade had the highest expression level at meristem. Cis-elements in the promoter ofMsTCPswere also predicted, the results indicated that most of theMsTCPswill be induced by phytohormone and stress treatments, especially by ABA-related stimulus including salinity stress. We found 20 out of 23MsTCPswere up-regulated in 200 mM NaCl treatment, andMsTCP3/14/15/18were significantly induced by 10 μM KCl, a K+deficiency treatment. Fourteen non-redundantMsTCPscontained miR319 target site, 11 of them were upregulated inMIM319transgenic alfalfa, and among them four (MsTCP3/4/10A/B) genes were directly degraded by miR319.MIM319transgene alfalfa plants showed a salt sensitive phenotype, which caused by a lower content of potassium in alfalfa at least partly. The expression of potassium transported related genes showed significantly higher expression inMIM319plants.ConclusionsWe systematically analyzes theMsTCPgene family at a genome-wide level and reported that miR319-TCPsmodel played a function in K+up-taking and/ or transportation especially in salt stress. The study provide valuable information for future study ofTCPgenes in alfalfa and supplies candidate genes for salt-tolerance alfalfa molecular-assisted breeding.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12870-023-04318-4.