1949年是中國政治史上關鍵性的一年，多年的國、共內戰，終告塵埃落定，共黨席捲大陸，國府則播遷來台。處此風雨飄搖之際，一部分對國、共兩黨均不滿的政治人物、知識份子；在美國和李宗仁的支持下，雲集香江一隅，首揭反國、共兩黨大旗，標榜反共、反蔣，堅持民主自由的第三勢力主張，正式在香港展開，此即當年曾盛極一時，喧騰不已的第三勢力運動。 基本上，五○年代的第三勢力運動，是美蘇冷戰結構下的一環，其背後有美國援助；以及反蔣勢力李宗仁等之奧援，故有其錯綜複雜的國內外背景因素存在。時第三勢力的要角有張發奎、顧孟餘、張君勱、左舜生、李璜、張國燾、許崇智、伍憲子、李微塵、童冠賢、邱昌渭、謝澄平等，這些人分屬民、青兩黨，部分為國民黨及桂系政治人物。 綜觀五○年代在香港的第三勢力運動，其中以青年黨是較具代表性和夠份量的，一則其行動最早；再則其初期的《自由陣線》集團和後來的《聯合評論》集團，在具體活動力與第三勢力理論闡述上，算是比較成功的，而彼時香港第三勢力運動的代表刊物，也以《自由陣線》和《聯合評論》最具代表性。而此二刊物均以青年黨領袖左舜生為主導，所以欲研究當年在香港從事第三勢力之底蘊，左舜生都是最具關鍵性的角色。是以本文之作，即以左舜生為研究對象，探討其當年參與香港第三勢力運動之經緯始末。

1949 was a year of political chaos and turbulence in China. The extended civil war between the Nationalists and the Communists was finally ended. The Communists occupied the whole mainland China, and the Nationalist government quickly evacuated to Taiwan. In this desperate era, certain politicians and intellectuals were unsatisfied with both the parties under the support of United States and Li Tsung-jen. These dissident politicians and intellectuals gathered in Hong Kong. They were against both Nationalist and Communist Parties, and they were also against Chiang Kai-shek. In the 1950s, they declared a democratic freedom faction, called the Third Force Movement, and they reached their height in Hong Kong. Looked at from the movement of the third force in the 1950s in Hong Kong, the Chinese Youth Party is more representative and certainly influential. It is because the party was first effectively mobilized. Besides, its “Freedom Front” Group and later “United Review” Group were relatively successful in terms of its theoretical explanation of the Third Force and its capacity of valid mobilization. Both “Freedom Front” and “United Review” were also representative publications of the Third Force Movement in Hong Kong. These two publications are dominated by the CYP leader, Tso Shun-sheng. So, if we want to study the role of the Third Force in Hong Kong, Tso Shun-sheng is the most critical character. The main purpose of this article is to study Tso Shun-sheng’s participation in the movement and the whole story of the Third Force in Hong Kong.