Determination of the grain geometry is an important step in the design of solid propellant rocket motors. The performance prediction of the solid rocket motor can be achieved easily if the burnback steps of the grain are known. fit this study, grain burnback analysis for 3-D grain geometries wits investigated. The method used was solid modeling of the propellant grain for predefined intervals of burnback. In this method, the initial grain geometry was modeled parametrically using CAD software. For every burn step, the parameters were adapted and the new gram geometry was modeled. By analyzing these geometries, burn area change of the grain geometry was obtained. Using this data and internal ballistic parameters, the performance of the solid propellant rocket motor in terms of motor pressure was achieved. The comparison between the results from this study and the results front the actual rocket motor tests shows that the procedure that was developed can be Successfully used for the preliminary design of a solid propellant rocket motor. (C) 2008 Elsevier Masson SAS. All rights reserved.