本文首先回顧了明清以來的五言古詩的聲調說，並認為明清詩家的聲調大都以少數詩作為例作說明，難見唐人五古的全貌。本文嘗試以統計的方法，較全面的檢視唐人五古平仄格調的規範，並認為五古之作分為新式的五古和仿古的五古。仿古詩作故無格律可言，但新式五古最基本的規律則在第二字黏對的講求。但這一規律必不是如近體詩一般，牢不可破，反而詩中允許一、二失黏失對及偶用律句律聯才是常式。 其次，本文在統計過程中也發現，王力以黏對為新式五古的要件，以此為準，他認為王維、李頎、孟浩然、劉長卿等人的五古為新式五古，李白、杜甫的五古為仿古之作，差不多完全不受格律的束縛，王力的說法是不正確的。 最後，本文也指出，盛唐新式五古雖然有格律化的傾向，但古詩之格律化並非如律詩之平仄不可差以毫釐，因此，劉長卿〈宿懷仁縣南湖寄東海荀處士〉一首五古，其格律整齊如排律，只是唐人五古中的特例，不足為式。

This paper reviews the tone pattern theories of the five-character poem of Ming and Ching Dynasties and then investigates the tone patterns of more than one thousand poems by prime Tang poets. It is the finding of this article that the tone pattern of five-character poems by prime Tang poets can be divided into two types, the so-called new five- character poem and old five-character poem. The present paper also indicates that the so-called new five-character poem must follow the regulation that the tone of the second character of each couplet must be opposite with each other and must keep same with the second character of the first line of the following couplet. Lastly, this paper finds that the fore-mentioned regulation is not abided by the Tang poets strictly. There is some leeway in between. Poets sometimes use their freedom in writing poems in term of metrical pattern.