On 7, December 1941, Japan attacked Pearl Harbor, the American naval base in the Pacific Ocean, and the Pacific War broke out. From this day, the Japanese authorities supervised the Taiwan theatre more and more systematically. In the beginning of 1942, "Taiwan Theatre Association" was established, which was to inspect the performances of all theatre troupes, to promote the Japanization policy. This essay presents firstly the social conditions of Taiwan around the time of the Pacific War. Then we will focus on the local amateur Youth Drama troupes and "Theatre Volunteer Corps" (Engeki tenshin tai) assigned by the Japanese authorities, by analyzing the development, performances, training and purposes of performance of these theatrical companies, in order to understand the situation of Taiwan westernized theatre ("New Drama") under the control of the Japanese authorities during 1941 to 1945, and its influences. From the study, the writer finds that since the Japanese authorities would like the performing groups to well comprehend the motif and purpose of Japanization, local amateur Youth Drama troupes as well as "Theatre Volunteer Corps" assigned by the Japanese authorities offered some courses on acting and theatrical techniques. The authorities also edited some collections of scripts and gave a course of dramaturgy. As most of the motives of these scripts focused on upgrading culture and promoting the content of Japanization, they neglected the uniqueness of individuals. However, with the performances of "Theatre Volunteer Corps" and local amateur Youth Drama troupes, more people could see the New Drama, and consequently the number of spectators increased. These should help the public accept the spoken drama after 1945.