Abstract: The grain size characteristics of the surface detrital sediments near the southern margin of Yap trench and their implications for sediment provenance were studied. Results show that the sediments are dominated by silt and clay in the region. Using the method of grain size component separation, four components, M1, M2, M3 and M4, were separated from fine to coarse. Among them, M1 and M2 are wind dust, which are distributed throughout the study area. M3 and M4 are pyroclast and siliceous bioclast mainly distributed near the Yapu Trench and West Caroline Trough. The detrital particles are rather coarse in the Yap Trench and the West Caroline Trough, whereas the kurtosis figure is small and the sorting is poor, indicating a complex sediment source; the sediments in the West Caroline basin are relatively fine, with low kurtosis and poor sorting, showing a relatively complex material source; whereas the sediments on the West Caroline ridge are the finest with high kurtosis and good sorting, suggesting a rather simple sediment source. From the ridge, basin to the trough and trench, the clastic sediments gradually become coarser, and poorly sorted, with the provenance gradually becoming more complex. It suggests that the distribution of mineral composition of sediments are closely related to the tectonic environment.