A nonthermal plasma jet is operated at atmospheric pressure inside a vacuum chamber filled with nitrogen gas. Various chemical compounds are fabricated from nitrogen and water molecules in plasma jet with varying oxygen content. Detailed theoretical investigation of these chemical compounds is carried out in terms of different oxygen ratio ξ. Experimental measurements are also carried out for comparison with theoretical results. Hydroxyl molecules are mostly generated at surface of water, and some of them can penetrate into water. The density of hydroxyl molecules has its maximum without oxygen, and decreases to zero as ξ increases to 0.25. The density of the ammonia of NH3 also deceases as ξ increases to 0.25. On the other hand, theory and experiment show that the density of the NO3 increases drastically as ξ increases to 0.25. The hydrogen peroxide density in plasma activated water deceases, reaches its minimum value at ξ = 0.05, and then increases again, as ξ increases from a small value to a large value. The pH value of the plasma activated water, which is slightly changed to alkali without oxygen, decreases as ξ increases.