Abstract: Applying the well-distributed statistic sample survey and tree trunk analysis method, this paper makes a research into the seriousness of Cronartium ribicola Fischer in the Pinus armandii forests in Dali.It defines the disease grade, growth capacity, loss amount and loss rate, as wall as the related index laws of each disease index number(x)for its loss capacity(y), thus inferring the loss rate of Cronartium ribicola,economic value and the estimated model of prevention and treatment indexes.