Heavy rain battered Sichuan Province for the past two days, the provincial flood control and drought relief headquarters.
Rescuers have been sent to search for the missing woman in Guanzhuang Township of Guangyuan City, state-run Xinhua news agency said.
Local governments have relocated about 2,700 residents to avoid risks of geological disasters.
The earthquake-stricken Ya'an City, which was jolted by a 7.0-magnitude quake on April 20 this year, also received strong storms.
The Sichuan Provincial Meteorological Bureau forecast that the province will receive strong rainfall on Thursday and Friday. It also issued an alert on flood and landslide risks.