Abstract: The general relationship among biomass, net production and life expectancy of leaves, according to the changing of the forest and components of trees in biomass, growth and mortality of leaf populations and mathematical principles of population ecology, is developed: Pn =lnlxB/X, where Pn is net production, lx age-specific survivorship, B biomass and X life expectancy of leaves. When a population is at this equilibrium, Pn =0.693·B/X the relation becomes the common expression by which almost all the ecologists are now using to calculate leaf net primary production from the data of life expectancy when a population has a survivorship of 36.8%. Also it is proved that the common expression, only being used in a particular situation, now accepted and used widely to be user′s confusion of leaf life expectancy with leaf turnover time, the use of the method appears to increase the results by as high as 30% or more. Two case studies are discussed here to show that, an overestimation of net primary production is unavoidable by using life expectancy of 0—1 age-class to compute it. The formula proposed in this paper is used to correct some of the calculated values of net production. The results show that Corrected values are well in accordance with those observed in practical situation.