The CoS2 powder is a kind of typical cathode material for the thermal battery. However, its poor chemical stability is easy to cause the failure. The failed CoS2 can lead to serious degradation of the electrochemical and security performance of the thermal battery. In this paper, the failure mechanism and renovation method of CoS2 powder synthesized by solid-state method are researched. The failure of CoS2 powder is caused by the chemical reaction with moisture and oxygen. The crucial factor leading to failure is moisture rather than oxygen, thus the failure of CoS2 powder can be prevent by controlling the humidity in the storage environment. The failure powder can be renovated and transformed into CoS2 after be calcined with appropriate proportion sulfur powder.