Abstract: In the thirteen months from August 193.3 to August 1934 Omeishan registered 9225mm. of rainfall. This amount is exceptionally heavy for a mountain which is not more than 3100m. in height and situated in (innermost China), not far from Chengtu. This extraordinarily heavy Frecipitation has heen found to he caused by the interaclion of a multiple of factors, such as topography, convection and the number of cyclones. High mountains forced the SW, or SE. monsoon to ascend, while ascending the relative humidity of the marine air is increased and when this humid air is forced to rise still higher either by cenvection or by the undercutting of cold air from the NW. precipitation would result This plusthe fact that Omeishan is on the tracks of shallow depressions, or even situated in the region where shallow depressions are formed, caused precipitation to be extraordinarily heavy.