This paper evaluates the mechanical properties of amorphous silicon carbon nitride (a-SiC${}_x$N${}_y$) films with different atomic ratios via molecular dynamics simulation. The Si-C-N ternary amorphous model is constructed using ReaxFF potential and melt-quenching method. The results demonstrate that the density range of constructed model spans a wide range of densities (2.247–2.831 g/cm³). The short- and medium-range order of the constructed a-SiC${}_x$N${}_y$ structures show a good correlation with the experimental observations. Based on the structural feasibility, the elastoplastic performance is analyzed. There is significant ductility during the uniaxial tension process of a-SiC${}_x$N${}_y$, except for Si(CN${}_2$)${}_2$. The calculated elastic modulus ranges from 206.80 GPa to 393.58 GPa, close to the experimental values of coating films. In addition, the elastic modulus of a-SiC${}_x$N${}_y$ does not change monotonically with the carbon or silicon content but is related to the atomic ratio. This article provides an understanding of the chemical composition dependence of the mechanical properties of amorphous compounds at the molecular level.