Deflection system for a gas stream 11 in an exhaust nozzle 10 of a flying craft, comprising fixed structural housings 18,20 which extend perpendicularly to the gas stream 11 and which are fed with deflection gas through one of their ends external to the nozzle 10, these housings 18,20 containing in their side walls 22,28 gas injection slits 23,30 oriented in oblique directions 24,26 relative to the gas stream 11, and controlled means for the adjustable closure of these slits 23,30.