Method for treating the surface of a moving substrate, in a facility comprising - an enclosure (10; 110; 210); - a support (20; 120; 220) for the substrate, received in said enclosure; - a counter-electrode (20; 120; 220); - at least one head (30; 130 1 -130 n; 230), defining an inner volume open in the direction of the support, said head being provided with - at least one electrode (8, 8', 8") suitable for cooperating with said counter-electrode in order to create an electrical discharge; - means for diffusing, for diffusing an inert gas towards said support; and - means for injecting (7, 7', 7"), separate from the means for diffusing, for injecting at least one active gas mixture towards said support, with this active gas mixture comprising a reactive gas capable of being activated by said electrical discharge; - the means for injecting being positioned between the means for diffusing and the support; method in which (i) both the inert gas and the active gas mixture are introduced towards said support, in such a way as to thrust the active gas mixture against said support; (ii) the reactive gas is activated in said electrical discharge and the surface of said moving substrate is treated; (iii) the gaseous atmosphere from the inner volume is discharged via said outlet, said gaseous atmosphere comprising a fraction of the inert gas and the active gas mixture; characterised in that the head and the support define at least one outlet for the inert gas and/or the active gas mixture and in that (iv) the effective cross-section of the outlet is adjusted and/or the total flow rate of the inert gas and the active gas mixture is adjusted, in such a way that the difference in pressures between the inner volume of each head and the inner volume of the enclosure is greater than 10 Pascal, knowing that the steps (i) to (iv) are not necessarily chronological. - an enclosure (10; 110; 210); - a support (20; 120; 220) for the substrate, received in said enclosure; - a counter-electrode (20; 120; 220); - at least one head (30; 130 1 -130 n; 230), defining an inner volume open in the direction of the support, said head being provided with - at least one electrode (8, 8', 8") suitable for cooperating with said counter-electrode in order to create an electrical discharge; - means for diffusing, for diffusing an inert gas towards said support; and - means for injecting (7, 7', 7"), separate from the means for diffusing, for injecting at least one active gas mixture towards said support, with this active gas mixture comprising a reactive gas capable of being activated by said electrical discharge; - the means for injecting being positioned between the means for diffusing and the support; (i) both the inert gas and the active gas mixture are introduced towards said support, in such a way as to thrust the active gas mixture against said support; (ii) the reactive gas is activated in said electrical discharge and the surface of said moving substrate is treated; (iii) the gaseous atmosphere from the inner volume is discharged via said outlet, said gaseous atmosphere comprising a fraction of the inert gas and the active gas mixture; characterised in that the head and the support define at least one outlet for the inert gas and/or the active gas mixture and in that (iv) the effective cross-section of the outlet is adjusted and/or the total flow rate of the inert gas and the active gas mixture is adjusted, in such a way that the difference in pressures between the inner volume of each head and the inner volume of the enclosure is greater than 10 Pascal,