This invention provides a structure for gunpowder charge in multi-frac composite perforation devices that is easy to assemble and transport while the charge volume of gunpowder is increased. In one embodiment of the present invention, an triplet outer gunpowder box is attached onto the outer wall of the charge frame and comprises one middle gunpowder box charged with gunpowder of certain burning rate, and two side-hung gunpowder boxes charged with gunpowder of another burning rate. The two side-hung gunpowder boxes are separately located on the two sides of the middle gunpowder box and are connected with the middle gunpowder box as a unit. The middle gunpowder box is located at a position corresponding to the perforating charge, and has an inner groove for orienting the perforating charge and a through hole through which the jet flow passes.