Abstract: This paper presents a new increase curve,■, for predicting development indexes, and deduces the calculation formulas of Q1 ~ t,tm, Qtmax and RPR. The changing characteristics of the Qt ~ t relation of the iflerease curve are studied through the use of figures. It is discovered that when the product of production time (t) and production rate (Qt) reaches maximum value (tQtmax), the ratio of accumulative production (Np(tQt)max) and maximum recoverable reserves (Nrmax) identically equals to 0.5, i.e. ■,which is termed as the 0. 5 criterion numeral of the new increase curve Np for predicting development indexes. The methods for calculating parameters such as Nrmax, b and a with actual data are proposed. A calculation in thc Shuanghe oilfield shows that the new increase curve is practical and accurate.