The paper mainly discusses the nature of linguistic signs in Saussure’s Course in General Linguistics. In the book, Saussure promoted semiology and regarded language as a system of signs and expounded the basic features of language from the aspect of semiology. In Saussure’s opinion, one of the most important characteristics of linguistic signs is arbitrariness. Saussure regarded the arbitrariness of the sign as"first principle."At the same time, Saussure also discussed the linear character of the linguistic signs as well as the invariability and variability of linguistic signs.