The study aimed to isolate and screen high-efficiency potassium solubilizing bacteria (KSB), and to quantify the effects of KSB application on plant yield and quality. The KSB strains were screened by silicate bacteria media from the rhizosphere soil of alfalfa (Medicago sativa), and subsequently the strains were identified by morphological, 16S rDNA sequence, and physiological and biochemical analysis. Pot experiments were conducted to evaluate the effect of inoculation with KSB strains on the yield and quality of alfalfa. Two high-efficiency KSB strains XLT-4 and XLT-7 were obtained with potassium solubilization rates of 10.53% and 9.75%>CK, and identified as Priestia megaterium and Peribacillus frigoritolerans, respectively. These two KSB strains had the metabolic capacity for phosphorus solubilization, siderophore-production and indole acetic acid secretion. Inoculation with XLT-4 and XLT-7 significantly increased plant height, root length, dry and fresh weight above ground and below ground, root activity, the contents of P, K and crude protein in leaves, while the contents of neutral detergent fiber and acid detergent fiber were significantly lower than in CK plants. In addition, the inoculation of the two KSB also improved the enzyme activity and available potassium content in alfalfa rhizosphere soil. In this study, the two KSB strains made a major contribution to improving the yield and quality of alfalfa, and these two organisms are high quality strain resources for the development of microbial preparations.