Using common quality specifications, the prediction equations for calculation motor octane number (MON) and research octane number (RON) were proposed, including distillation range, density, aromatic content, and olefinic content or bromine value. From a large number of refineries and literature data, about 70% of the sample error is less than 1.2 when MON is calculated directly by means of these prediction equations, and more than 81% of error is less than 1.8 by RON being calculated. Therefore, the ON can be calculated by these equations. It shows that the error of the prediction equations meet the standard requirement. The equations are a rapid, simple and wide-application method for the calculation of ON. They have something referential values for product quality control in petroleum refinery operation．