Abstract: The filling process of RTM for the two step 3D braid shell preform with a varying section was investigated theoretically by employing a calculating method of divide-integration. Several formulations related to the resinvelocity, resin filling time and resin flow pressure were proposed accurately. Good agreement was found between theexperimental result s and numerical predictive values. The deduced formulations could provide the theoretical basisfor suitably designing RTM filling parameters.