According to the seismic data (m b≥5.0) from 1977 to 1991 and the focal mechanisms of 68 earthquakes from 1961 to 1991, the characters of seismicity and stress field in Okinawa Trough and Ryukyu regions are discussed in this paper, and the paper suggests that: 1) the Tokara Channel fault belt is a fault belt with seismicity, cutting through lithosphere. 2) The different stress state in the both subducting slabs on the both sides of Tokara Channel fault belt are caused by the difference of subducting depth of the both slabs. 3) The seismicity and stress field in the Okinawa Trough and Ryukyu regions are related not only to the subduction of the Philippine Sea Plate but also to the self-expanding action of Okinawa Trough.