Aluminum-lithium alloy powder has broad application prospects in the field of energetic materials due to its good thermal performance. However, the high reactivity of lithium and the incompactness of the surface oxide layer result in the continuous oxidation of the active metal during storage, thereby deteriorating the thermal performance of the powder. In this paper, a layer of polystyrene (PS) was successfully coated on the surface of Al-10Li (10 wt.%) alloy powder by in-situ polymerization of styrene (St). According to an orthogonal test, the optimum coating conditions for protection factor were as follows: m(St)/m(Al-10Li) was 1 : 1; m(AIBN)/m(St) was 5 %; the reaction temperature was 75 degrees C; the reaction time was 4 h. The structure, surface morphology and thermal properties were characterized by XPS, FTIR, SEM and TG-DTA. Furthermore, the aging stability of powders were studied by TG-DTA. The results showed that the decay rate of the weight increase of the active metal of Al-10Li alloy powder decreased significantly after coating, which demonstrated that the polystyrene coating effectively protected the active metal of Al-10Li alloy powder, prevented pre-oxidation of Al-10Li alloy powder in air and improved its storage stability.