Fibrous preform for a hollow blade of a turbomachine, such a hollow blade and a method for manufacturing such a hollow blade. The preform comprises a first fibrous structure (41') obtained by three-dimensional weaving and comprising at least one main longitudinal portion (46, 47) able to form essentially an air foil pressure-face wall, a second fibrous structure (42') obtained by three-dimensional weaving and comprising at least one main longitudinal portion able to form essentially an air foil suction-face wall; the first and second fibrous structures (41, 42) furthermore each comprising a first connecting zone (43), extending along the front edge of their respective main longitudinal portion (46), secured to one another and forming a first connecting portion (43) of the preform and a second connecting zone (44), extending along the rear edge of their respective main longitudinal portion (46, 47), secured one to the other and forming a second connecting portion of the preform (44); the main longitudinal portions (46, 47) of the first and second fibrous structures (41', 42') being non-attached so as to leave between said main longitudinal portions (46, 47) a space (D2) able to form an air foil hollow.