Abstract: The slope stability of landfill is increasingly concerned with the increase of waste production and landfill height. It is of great importance to monitor the slope stability during landfill operation. This study presents field monitoring results from a large landfill, in which slope failure and piping of sludge pond took place in June 2008 and in February 2009, respectively. The field monitoring items include leachate level, deep lateral displacement, surface horizontal displacement and vertical displacement at the landfill. The monitoring results are analyzed on the basis of the records of rainfall, operating conditions and contingency measures. The monitoring results demonstrate that the high leachate level within the landfill is a major factor leading to the slope failure, and the horizontal displacement rate is the most sensitive index indicating the slope stability. According to the statistic analysis, the early warning value of horizontal displacement rate is deduced as 10 mm/d. It will provide important experience and guidance for the safety monitoring of MSW landfills.