Considerable effort has been devoted to the Li–N–H system for solid-state hydrogen storage. However, the desorption mechanism is still unclear, the desorption kinetics is too low, and the desorption temperature is too high for practical considerations. Here, the characteristics of LiNH2 and a (LiNH2 + LiH) mixture were comparatively studied by simultaneous thermogravimetry, differential scanning calorimetry and mass spectrometry for further understanding of H2 desorption in the (LiNH2 + LiH) system. Both mechanical milling and chemical addition were noted to influence the decomposition kinetics of LiNH2. Mass spectrometry and thermal analysis of (LiNH2 + LiH) mixtures indicate that approximately 5 mass% of H2 is released after 4 h of milling without any apparent release of NH3, whereas insufficient mixing of the two compounds cannot stop the release of NH3 from the mixture. Chemical additions, Mn, V, MnO2 and V2O5, promote the thermal decomposition of LiNH2, but show insignificant effect on hydrogen desorption of the (LiNH2 + LiH) mixture.