Eeckhout (2004)的一般均衡理論可解釋吉伯特定理中的都市成長過程與分佈。該文對於模型中的主要驅動力之一的地方外部性，並無進一步探討。本研究的目的是分析地方外部性形式特質與都市成長過程及人口分佈的關係。本研究對模型中之地方外部性進行延伸分析，發現當地方外部性中的產出都市人口彈性固定時，一般均衡理論中的隨機生產過程可推導出比例成長的都市人口；同時，都市人口的上尾端分布會趨近於普瑞夫定理．此結果在Eeckhout (2004)中未提出。此外，地方外部性中的擁塞成本越大，估計的吉尼係數越小，都市間人口差異越小。該理論隱含當產出都市人口彈性為負時，技術衝擊越大都市規模越大；當擁擠成本主導淨地方外部性時，技術衝擊越大都市規模越大。

Ageneral equilibrium model proposed in Eeckhout (2004) explains Gibrat's law in growth process and size distribution of cities. One of the driving forces in the modelis local externality; however there is lack of further exploration of this key driving force. The purpose of this paper is to examine the feature and relation between local externality and the resulted growth process as well as size distribution; this is not discussed in Eeckhout (2004). This paper provides an extension of local externality and finds that the theory could generate proportionate growth of cities and Zipf's law in its tail only if the size elasticity of production in local externality is a constant. This result shows the condition of the theory in explaining the empirical size distribution of cities which is not examined in Eeckhout (2004). We also finds that an increase of congestion cost will lead to more evenly distributed cities.Moreover, the theory implies that larger technologyshocks lead to larger cities when the size elasticity of production is negative; larger technologyshocks lead to bigger cities if the congesting cost dominates the net local externalities.