Rest-grazing measures during the regreen-up period can effectively improve alpine grassland productivity, in order to understand their effects on nitrogen mineralisation and microorganisms. Using the alpine meadow in Dawu Township, Maqin County, as the experimental site, five rest-grazing times were set up, namely CK (grazing), 20 d, 30 d, 40 d and 50 d, and the dynamic changes of soil microbial biomass and available nitrogen were investigated in the forage growing season (May-September). The results showed that both soil microbial biomass carbon (SMBC, Soil Microbial Biomass Carbon) and soil microbial biomass nitrogen (SMBN, Soil Microbial Biomass Nitrogen) presented an upward trend with the increase of the rest-grazing time. The SMBC increased by 22.49% and 123.33% under 50 d of rest-grazing compared to CK at the early stage of growth (May and June), and the content was higher under 40 d of rest-grazing at the end of growth. The SMBN was significantly higher under 40 d of rest-grazing in May and higher under 50 d of rest-grazing in the rest of the months. Soil ammonium nitrogen (NH⁺₄-N) and nitrate nitrogen (NO^-₃-N) showed a trend of increasing and then decreasing in the growing season. In most cases, the soil NH⁺₄-N content was higher than that of the CK for 30 d of rest-grazing; the effect of different rest-grazing times on soil NO^-₃-N content was not obvious. Soil N mineralisation rate varied significantly between months, but generally showed a trend of higher soil N mineralisation rate for 30-40 d of rest-grazing and lower for CK. Therefore, appropriate rest-grazing activities in the regreen-up period in alpine meadows of the three-river source region are conducive to the conversion of organic nitrogen.