Using the Flexible Particle (FLEXPART) model, a Lagrangian particle dispersion model, and the areal source-receptor attribution method, the moisture sources and quantification of the contribution from moisture sources were studied during the supertyphoon Rammasun landfalling from 0600 UTC 17 July 2014 to 0600 UTC 19 July 2014. The results indicate that the vast majority of target particles are mainly from the southwest and east of the target precipitation region. The former originated from the relatively lower atmospheric layers and can be traced back to regions such as the Arabian Sea and the Bay of Bengal, while the particle height does not change much in transit. The latter can be traced back to the Western Pacific Ocean and the particles were relatively higher in initial position with height reduction during transportation. The South China Sea region (C) made the largest contribution, followed by the target precipitation region (T), meanwhile the Bay of Bengal (B) and the south of the Western Pacific region (D) both contributed similar amounts less than the region T. The greater contribution of region C and T to the precipitation during Rammasun landfalling is attributed to its higher Uptake (especially region C) and lower Loss along the way (especially region T). The Uptake in region B is higher than that in region D, but the Unreleased proportion of the former is significantly higher than that of the latter. Meanwhile, the Loss along the way of the two is equivalent, resulting in their final roughly equal contribution to the target precipitation area. Although the Uptake in the Arabian Sea region (A) is also substantial, its ultimate contribution to the target precipitation region is dramatically reduced due to significant consumption along the way. The FLEXPART mode and the areal source-receptor attribution method can reveal the characteristics of moisture sources related to tropical cyclone precipitation more clearly and quantitatively than the previous commonly used circulation and water vapor flux analysis.