The invention relates to a slope water-soil loss experiment device and method under combined extreme meteorological conditions. The experiment device comprises an experiment table, a combined extreme environment simulation unit and a control system unit, wherein the experiment table comprises a bottom base, a slope base plate, a downstream baffle plate, soil block standard elements and an experiment table regulating device; the combined extreme environment simulation unit comprises a rainfall simulation device, an air field simulation device, a freezing rain simulation device, a snowfall simulation device, a sunlight simulation device, an air temperature simulation device and an overland flow simulation device; the control system unit comprises a power supply system, a water supply system and a signal acquisition and processing system. According to the invention, the slope water-soil loss experiment device and method under combined extreme meteorological conditions perform indoor simulation and measurement of a slope water body loss situation under a single or combined extreme meteorological conditions of rain storm, rain and snow, freezing rain, flood, drought, high temperature and the like, can achieve accurate and reliable results, and can be widely applied to water-soil loss monitoring, principle analysis and governance under complex variable meteorological conditions.