According to the observations obtained at Tiebujia Animal Husbandry Meteorological Station in Qinghai province,the biological features of natural herbage growth,and the meteorological condition during different growth and development periods,the herbage yield is decomposed into the average economical yield and climatic yield.The animal husbandry meteorological index,or waterheat index,is designed and calculated.The formation rule of the natural harbage yield is analysed,and the yield in different stages is simulated.The forecasting model can be used to calculate the total yield,accumulative velocity of yield and the potential maximum yield.