Abstract: Breeding and cultivating high-quality legumes is an important way to develop livestock agriculture on alpine grasslands. Vicia unijuga is a perennial legume with high feeding value. Research on its hay yield and nutrient dynamics is needed to inform its production and utilization as forage. A field trial has been conducted on Gannan alpine grasslands with the aim of investigating the feeding value of V. unijuga at different growth stages. Samples were taken at branching, squaring, 20% bloom and 80% bloom stages. Measurements were made to determine forage yield, crude protein (CP) and water soluble carbohydrate (WSC) contents, as well as the levels of ash and various other mineral elements. Results showed that hay yield increased with growth stage but that CP levels were higher at the early growth stage. While CP decreased at the late growth stage (80% bloom), WSC contents reached their highest level at this point. Ash levels showed a single-peak curve variation across the different growth stages. However, mineral element contents varied less consistently. P, Zn, Ca and Mn varied in half-peak or peak type curves, Na and Mg in linear type, K and Cu in wave type. In conclusion, CP contents reached the levels of first-class forage grasses in America. Hay yield and WSC levels were highest at the 80% bloom stage, at which point the levels of P, K, Na, Mg, Mn and Zn are sufficient to satisfy the basic needs of livestock. Grey relational analysis and weight assignment methods were used to evaluate the above results. This analysis showed that the evaluation index was highest at the 80% bloom stage, which is thus the optimal cutting point of V. unijuga for alpine grassland agriculture.