A process for producing ammonia synthesis gas from a hydrocarboncontaining feedstock in a front-end, the process comprising the steps of: steam reforming of said feedstock, obtaining a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide; a treatment of said synthesis gas including shift of carbon monoxide and subsequent removal of carbon dioxide, characterized in that: the shift of the synthesis gas includes a step of high-temperature shift with an iron-based catalyst; said steam reforming comprises: a first reforming step including a primary steam reforming and optionally including a pre-reforming before said primary steam reforming, thus obtaining a first reformed gas; a secondary reforming fired with a stream of an oxidant, thus obtaining a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide; said first reforming step and said secondary reforming being performed in series, said secondary reforming being carried out by using oxygen or enriched air comprising at least 50% oxygen, as the oxidant stream; and wherein the synthesis gas obtained after said secondary reforming being then mixed with steam, prior to its feeding to high-temperature shift, so that the global steam-to-carbon molar ratio of the front end is 1.5 to 2.6, the global steam-to-carbon molar ratio being the ratio between the moles of steam and moles of carbon which are admitted to the process, including any feed of hydrocarbon and any feed of steam up to the inlet of the high temperature shift. steam reforming of said feedstock, obtaining a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide; a treatment of said synthesis gas including shift of carbon monoxide and subsequent removal of carbon dioxide, characterized in that: the shift of the synthesis gas includes a step of high-temperature shift with an iron-based catalyst; said steam reforming comprises: a first reforming step including a primary steam reforming and optionally including a pre-reforming before said primary steam reforming, thus obtaining a first reformed gas; a secondary reforming fired with a stream of an oxidant, thus obtaining a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide; said first reforming step and said secondary reforming being performed in series, said secondary reforming being carried out by using oxygen or enriched air comprising at least 50% oxygen, as the oxidant stream; and wherein the synthesis gas obtained after said secondary reforming being then mixed with steam, prior to its feeding to high-temperature shift, so that the global steam-to-carbon molar ratio of the front end is 1.5 to 2.6, the global steam-to-carbon molar ratio being the ratio between the moles of steam and moles of carbon which are admitted to the process, including any feed of hydrocarbon and any feed of steam up to the inlet of the high temperature shift. the shift of the synthesis gas includes a step of high-temperature shift with an iron-based catalyst; said steam reforming comprises: a first reforming step including a primary steam reforming and optionally including a pre-reforming before said primary steam reforming, thus obtaining a first reformed gas; a secondary reforming fired with a stream of an oxidant, thus obtaining a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide; said first reforming step and said secondary reforming being performed in series, said secondary reforming being carried out by using oxygen or enriched air comprising at least 50% oxygen, as the oxidant stream; and wherein the synthesis gas obtained after said secondary reforming being then mixed with steam, prior to its feeding to high-temperature shift, so that the global steam-to-carbon molar ratio of the front end is 1.5 to 2.6, the global steam-to-carbon molar ratio being the ratio between the moles of steam and moles of carbon which are admitted to the process, including any feed of hydrocarbon and any feed of steam up to the inlet of the high temperature shift. a first reforming step including a primary steam reforming and optionally including a pre-reforming before said primary steam reforming, thus obtaining a first reformed gas; a secondary reforming fired with a stream of an oxidant, thus obtaining a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide; said first reforming step and said secondary reforming being performed in series, said secondary reforming being carried out by using oxygen or enriched air comprising at least 50% oxygen, as the oxidant stream; and wherein the synthesis gas obtained after said secondary reforming being then mixed with steam, prior to its feeding to high-temperature shift, so that the global steam-to-carbon molar ratio of the front end is 1.5 to 2.6, the global steam-to-carbon molar ratio being the ratio between the moles of steam and moles of carbon which are admitted to the process, including any feed of hydrocarbon and any feed of steam up to the inlet of the high temperature shift.