The Xi-yan 西燕 was one of the warrior powers during the Shiliuguo 六國 period. They had tried to restore the dynasty of Qian-yan 前燕 and had successfully conquered Qian-qin 前秦 , captured its capital, Chang-an 長安, and almost captured its emperor Fu-jian 苻堅 . However, the Xi-yan 西燕 Still failed and decline ten years later. This research is merely trying to analyze the reason why it declined so fast , why it tamed out to be disorder , and examine the relations between its political and social structure which doomed the destiny of Xi-yan.