Abstract: The microstructures of FeNiCrAl alloy synthesized by thermite process was investigated by XRD, SEM, and TEM. The effect of Al content in thermites on the tensile properties of the alloy was also studied. Results show that the synthesized FeNiCrAl alloy is mainly composed of austenite phase when the thermite contain no more than 25.4wt.% Al content. The main component phase of the alloy turns into ferrite when the Al content comes to 26.6wt.%, meanwhile particle NiAl precipitates arise. With the Al content continues to increase, the particle NiAl phase is gradually replaced by the intertexture structure. Research shows that the formation of the intertexture structure is due to liquid spinodal decomposition. The elongation of the alloy decreases with the increase of the Al content in thermites. When the thermite contain 26.6wt.% Al content, the tensile strength of the alloy reaches its maximum performance, that is, 640.87 Mpa.