In order to explore the thermal stability of AlCrFeNiTi high entropy alloy, the as-cast AlCrFeNiTi high entropy alloy was synthesized by the vacuum arc melting under an argon atmosphere, and the hardness change of alloy in different heat treatments, including heating temperature and holding time was evaluated, and then the relationship between the hardness and microstructures of AlCrFeNiTi alloy was further discussed. Finally, the network model between heat treatments and hardness of AlCrFeNiTi alloy was built by the back propagation artificialSneuralSnetwork (BP-ANN) to predict the hardness of AlCrFeNiTi alloy. The results show that the as-cast AlCrFeNiTi high entropy alloy is composed of two body centered cubic structures, and typical dendrite, interdendrite and eutectic structure (α+β) microstructures are observed. Comparing with as-cast alloy, the microstructures and content of dendrite of alloy under different heating temperature (from 400 to 900℃) and holding time (from 0.5 to 10h) have no significantSchanges, and the hardnesses of these heat treated samples are all higher than HV400, which indicates the AlCrFeNiTi high entropy alloy has a good thermal stability. Furthermore, the established BP-ANN between heat treatments and hardness of AlCrFeNiTi alloy shows better precision and applicability and can be used to guide the industrial applications.