周代封國數以百計，在《史記‧十二諸侯年表》中列出十三家事蹟較詳者，其中壽命最長的為齊、燕兩國。燕國雖比齊稍短，但齊國在386B. C.已遭田氏所篡，而燕國從第一代諸侯到末任國君燕王喜算起前後四十二代，始終同一世系。戰國以前燕國一直是個默默無聞、地處偏僻的弱小國家，至戰國中期燕昭王廣招人才銳意改革，才躍升為強國，成為戰國七雄之一，在國際舞臺上嶄露頭角。何以一個原為偏弱的國家，處於兼併激烈的春秋戰國時代，非但沒有被時代洪爐所吞噬，還能存活如此之久，實是耐人尋味。本文即從地理環境、政治、經濟、軍事等各個角度，探討燕國國壽綿長的原因。

According to the 《史記．十二諸侯年表》, the Zhou dynasty held hundreds of vassal states, while the Qi and Yan were the countries which successfully last for a long period. Though Yan's longevity was a bit shorter than Qi, Qi was usurped by Tian Shi in 386B.C, while Yan kept maintaining its imperial power and family for 42 generations. Yan used to be an unknown and remote country before Zhan Guo (戰國) era, it became one of the seven strongest countries after the King of Yan Zhao made widely recruitment and reformation. It is interesting to know for what reasons that a poor and remote country could survive for such a long time, but not being ruined by other competitive opponents. This paper will probe into the reasons of Yan's longevity from the aspects of geographical environment, political, economic and military.