Calcium compounds with N and H are promising catalysts for NH3 conversion, and their epitaxial thin films provide a platform to quantitatively understand the catalytic activities. Here we report the selective epitaxial growth of Ca2NH and CaNH thin films by controlling the hydrogen partial pressure (P H2 ) during reactive magnetron sputtering. We find that the hydrogen charge states can be tuned by P H2 : Ca2NH containing H– is formed at P H2 < 0.04 Pa, while CaNH containing H+ is formed at P H2 > 0.04 Pa. In situ plasma emission spectroscopy reveals that the intensity of the Ca atomic emission (∼422 nm) decreases as P H2 increases, suggesting that Ca reacts with H2 and N2 to form Ca2NH at lower P H2 , whereas at higher P H2 , CaH x is first formed on the target surface and then sputtered to produce CaNH. This study provides a novel route to control the hydrogen charge states in Ca–N–H epitaxial thin films.