Four probiotic strains were used to ferment germinated highland barley, and the Lactobacillus acidophilus and Saccharomyces boulardii, which exhibited the highest viability after fermentation, were selected. Subsequently, a response surface test was applied to identify taste-enhancing additives, including concentrated orange juice, erythritol, and flaxseed oil. The optimal concentrations of these additives were 3.01%, 4.19%, and 0.52%, respectively. The stabilizing effects of β-glucan and four protein sources (whey, rice, pea, and soybean proteins) were assessed based on emulsion stability, and the combination of β-glucan and whey protein was identified as the most effective. Based on particle size and zeta potential analysis, the optimal β-glucan-to-whey protein ratio was determined to be 2:1. On this basis, a germinated highland barley probiotic beverage was developed. The results indicated that the total colony counts after simulated gastrointestinal digestion remained above 6 log CFU/mL, and the beverage was rich in dietary fiber and other nutrients.