A macroscopic kinetic model of the defect transformation and decomposition of a silicon nitride SiNx:H film during high temperature annealing is proposed in this article. It takes into account breaking of (SixNy)=Si:H and (SixNy)=N:H bonds with formation of dangling bonds, mobile atomic and molecular hydrogen and atomic nitrogen, diffusion of mobile species to the film surface and their evolution from the film. Numerical simulation of a set of equations describing these processes allows us to find distributions for both the 'free' hydrogen, 'free' nitrogen and the bound hydrogen ((SixNy)=Si:H and (SixNy)=N:H, and dangling bonds (SixNy)=Si and (SixNy) =N inside the film during high temperature treatment as a function of the annealing time. The results of the numerical simulations have been compared with experimental data. The fitting parameters of the model have been found. The analysis proposed can be applied to other hydrogen-containing thin films.