周平王東遷雒邑時，國力雖不能與西周盛世時相提並論，但京畿幅員猶廣，尚有太華、外方之間方六百里之地，憑藉西周舊業及東都儲積，平王若能勵精圖治，王室仍可興盛。然平王在位五十年之後，王室勢力卻呈現衰退現象，其後更是每況愈下，平王在位的五十年期間，是東周王室後續發展的關鍵，也是王室步向衰微的開始，其衰弱原因在東周史上誠極具重要性。本文分就王室繼承、平王施政情形、東遷前後之天下局勢等面向進行探討，探索上述因素與王室衰微間的關係。經研究後發現，主要有：一、平王在王位繼承的正統性有爭議，以致造成兩王並立，王室分裂。二、平王東遷，東遷後王室與諸侯國間上下關係已改變。三、平王施政欠佳，國人怨之。四、鄭國崛興，拓展勢力，王室無力號令等四點，是王室東遷後五十年所以日趨衰微之主要原因。

When Zhou royal (周王室) moved capital to east city, Luo Yi, (雒邑) national power of East Zhou (東周) was less than West Zhou's. (西周) But royal family still owned much land. The area of country's territory was wide. If Ping King (平王) could make great efforts to build the state, royal family had been strong. Actually, during fifty years of Ping King on his position, the power of royal was getting declining. The period of Ping King was the key point of developing for East Zhou. This period was also the start point of declining. The declining reasons were important in East Zhou history. This paper presents the declining reasons during fifty years after Ping King moved capital to east city. The main reasons include that the position of Ping King was argued, the relation between royal and vassals was changed after moving capital, the politics of Ping King not excellent, the power of vassals were getting mighty.