Robotized filament winding technology involves a robot that winds a roving impregnated by resin on a die along the directions of stresses the work-piece is submitted to in exercise. The robot moves a deposition head along a winding trajectory in order to deposit roving. The trajectory planning is a very critical aspect of robotized filament winding technology, since it is responsible for both the tension constancy and the winding time. The present work shows an original method to plan the winding trajectory of structural parts whose shape is obtained by sweeping a full section around a 3D closed not autointersecting curve. The trajectory is defined by offsetting this 3D curve of the distance needed to keep the tension on roving near to the value chosen to assure good mechanical performances of the manufactured composite parts. This trajectory allows to satisfy the constraints on the geometrical parameters of the winding trajectory (i.e. safety distance and winding angle) that assure to keep the value of tension near to the nominal one during winding. This means to assure an acceptable quality of the manufactured composite parts. Moreover, the planned trajectory allows to decrease strongly the winding time, when compared to the alternative methods of the trajectory planning.