The invention relates to a system for injecting pasty, semipasty or liquid waste into an incineration furnace with at least one base (4), said system comprising an injection body (25), provided with a waste supply chamber (28), means for injecting a pressurised gaseous fluid, a waste spray nozzle (33), having at least one waste injection channel and means for directing the injection body and/or the nozzle towards the base. Said system is characterised in that the means for injecting a pressurised gaseous fluid include at least one pressurised gaseous fluid supply chamber (26), provided around said waste supply chamber (28) and the nozzle (33) comprises a plurality of peripheral channels (27), connected to the pressurised gaseous fluid supply chamber (26) and arranged around the waste injection channel (33a), said peripheral channels (27) being convergently inclined in relation to the longitudinal axis (A) of said waste injection channel.