The present invention relates to a system for plugging a mould (2) for injection moulding of foamed plastic material, particularly EVA (ethylene vinyl acetate), comprising a guillotine device, in correspondence of the mould (2) injection port (3), said device being comprised of two hemi-guillotines (4, 5), laterally movable along a plane substantially perpendicular with respect to the advancement direction of injector (1) toward the mould (2) between a closed position and an open position, lateral movement of said hemi-guillotines (4, 5) being obtained by interaction with said injector (1) along its run toward the mould (2), means (6, 7) opposing against said lateral movement being provided, maintaining said hemi-guillotines (4, 5) in a normally closed position.