Abstract: A rarely seen cold wave hit Yunnan Province from March 31^st to April 2^nd, 2022. This study analyzes the formative factors of the cold wave based on the data of in situ observations, upper air observations and NCEP FNL. Meanwhile, the study also examines the situation fields and the lowest temperature by using the European Centre for Medium-Range Weather Forecasts (ECMWF) model. The result shows that this cold wave occurred in a negative phase of Arctic Oscillation, when there happened an abnormally strong Siberian High, and a large-scale two-trough-and-one-ridge circulation pattern in the Eurasian mid-and-high latitudes. Northerly wind behind the Eastern Asian trough piloted the low level cold air towards the south; meanwhile, the southern branch trough moved eastward and transported warm wet air towards Yunnan. The 700 hPa wind shear and near surface cold front jointly caused this cold wave when they invaded southward. The severe temperature drop was caused by the strong near surface cold air flux during the event. Furthermore, the strong vertical upward motion of the cold front rear and its corresponding adiabatic expansion cooling quickened the local temperature drop. A quantitative analysis of the factors causing the local temperature change in Kunming finds out that the horizontal temperature flux dominates the temperature drop in Kunming, followed by the non-adiabatic item. As for this cold wave, the ECMWF model was fairly good at forecasting the high-and-low-level circulation pattern and the geographical range of temperature drop, while less good at forecasting the strength of temperature decrease.