Using basic observational data and NCEP reanalysis data, a disastrous snowstorm weather of missing report in the northeast of Inner Mongolia was analyzed diagnostically. The results showed that this snowstorm weather process is different from the conceptual model in synoptic meteorology of snowstorm in Inner Mongolia. There is no powerful water vapour transport, the large value area of vertical ascending motion is concentrated between 850 hPa to 500 hPa, and the heavy snow has the mesoscale characters of short duration, great intensity, small range and serious disasters. In this process, the powerful warm advection of 850 hPa is cooperated with the weak and cold advection in the southwest airflow of 500 hPa, the temperature advection in the lower troposphere decreases with altitude which is of benefit to the construction of unstable stratification, the mergence and reinforcement of ground secondary cold front with cyclone and the intensive development of mesoscale low vortex of 850 hPa strengthen convergence ascending motion in the lower troposphere, and unstable energy release is the main cause of snowstorm. Finally, the “cold wedge” of boundary has some amplification effect on heavy snow.