Abstract: Based on conventional observation data, NCEP reanalysis data (2.5°×2.5°), a rare cold wave and low temperature weather process which occurred in Pingliang City of Gansu Province from 4 to 7 in April 2018 was done. The results show that: 1) the cold air source of this cold wave weather is in the ocean surface to the east of Novaya Zemlya. Five days before the cold wave broken out, there was an off-center polar vortex at 100 hPa in the Northern Hemisphere. During the outbreak period of cold wave, the polar vortex in the middle and upper troposphere occurred a split. Because the center of polar vortex near China was stronger, the cold weather was also stronger. 2) The type of this cold wave process belonged to the development of unstable trough which in the fore part of high-pressure ridge. The main influence systems of high altitude were high pressure ridge in Ural Mountain and low-pressure trough. The thermal and dynamic factors jointly promoted the development and eastward movement of the trough and the ridge. With the strengthening of northerly wind in front of the high-pressure ridge, the cold air behind the low-pressure trough violent erupted to the south. 3) Around the outbreak of the cold wave, the main cold air with secondary cold front affected the cold wave area in the form of splitting. The dynamic and thermal effects of the deformation field and surface trough were conducive to the formation of surface (secondary) cold front and the strengthening of surface cyclone. 4) the intensity of 500 hPa high altitude cold center and ground cold high pressure all reached or exceeded the corresponding index value of the regional cold wave in Gansu Province in April; before the cold wave broke out, Pingliang Prefecture was in an obvious warming environment. During the outbreak period, due to the influence of strong cold advection for a long time, the temperature of Pingliang Prefecture occurred a significant sustained reduction. Pingliang Prefecture has obvious ascending motion and adiabatic expansion cooling effect, which was conducive to the further intensification of the cooling weather. (5)The temporal and spatial evolution characteristics of the second wet also baroclinic term in the wet potential vortex could well describe the movement and development of cold air, which was conducive to the judgment and research of the cooling situation in the cold wave weather.