The invention belongs to the technical field of chemical engineering and particularly relates to a water vapor electrolytic process based system for joint production of ammonia and nitric acid. The system comprises a nitrogen generation unit, an ammonia synthesis unit, a nitric acid generation unit, and a solid oxide electrolyzer. The ammonia synthesis unit is used to provide the material ammonia and process vapor for the nitric acid generation unit, no ammonia is externally purchased for the nitric acid generation unit, meanwhile, a heat recovery boiler is eliminated. The reaction heat of the ammonia synthesis unit and the nitric acid generation unit is used to produce high temperature vapor, the high temperature vapor is applied to the solid oxide electrolyzer, the solid oxide electrolyzer produces hydrogen and oxygen, the hydrogen and the oxygen are applied to the ammonia synthesis unit and the nitric acid generation unit, so that a mode of joint production of ammonia and nitric acid by taking air and water as raw materials is achieved, no materials or fuels are externally purchased, only electric energy is used, so that the system has the characteristics of high integration, low production cost, single and convenient energy consumption, reasonable recovery of energy, less environment pollution, conformity to the international emission standard and the like, and has an excellent economic benefit and an excellent application prospect.