In general meaning, castle is a military facility which is used to defense alien enemies. The origin of the castle is probably arising with the generation of primitive society. Comparing with either ancient times or modern times, Samurai jidai which has more than 700 years’history is taken as the epoch-marker in the history of Japanese castle. As a force tool of governing class, Japanese castle is inseparable with its military function. During the history, all governing classes attached importance to the offensive and defensive function of castles. However, with the change of time, castles became not only military facilities but also the symbol of political authority. As a result of this, the practicability of Japanese castle was gradually weakened and the luxury which symbols authority began to be strengthened by daimyos.On the basis of working over both Chinese and Japanese literature, this thesis adopts culturology theories to analysis some relevant opinions on Japanese castle, attempting to expound the function and feature of Japanese castle in Samurai Jidai.This thesis consists of six chapters. The first chapter is the introduction. In this part, the author mainly introduces the research objectives and significance as well as some primary study on the function of Japanese castle. In the second chapter the author discusses the establishing background of Samurai Jidai and gives a general overview of Japanese castle in that period. The second chapter can be divided into three sections. Section one introduces the classification of Japanese castle. Section two represents the construction background. Section three outlines the development and reform of Japanese castle. The third chapter studies the attack and defense oriented castle from Kamakura Jidai to late Sengoku. The author sets forth the construction background, the classification, the function and the feature respectively in four sections. In Chapter four, the author investigates the authority oriented castle from late Sengoku to early Edo. There are four sections in this chapter. Section one introduces the turning point of the authority oriented castle. Section two is the classification of the authority oriented castle. Section three explores the function of the authority oriented castle and the last section summaries the feature of it. The fifth chapter analyzes reasons and features of the changeover of function of Japanese castle during Samurai Jidai. As well as this, the author develops a comparative study on the function of both Chinese and Japanese castles. The last chapter is the conclusion.The study of Japanese castle in samurai Jidai involves a numbers of areas. This thesis studies doesn’t research all of them, only choosing the military and political function as the objects. For another important economic function, the castle town, the author intends to do a further study on it in the future.