On the basis of data source acquisition, define September 1 to August 31 of the next year as a snow year, count the maximum number of consecutive snow days in a snow year as the number of consecutive snow days in the year (CSCD), record the total number of days from the first day to the last day in a snow year as the number of snow days in the year (SD), and record the cumulative number of snow days in a snow year as the number of snow days in the year (SCD), Record the ratio of snow days to snow period as the annual snow fluctuation rate (R);

On the basis of counting the number of consecutive snow days and snow periods each year, count the grids with snow records of more than 10 years (including 10 years), and the grids with snow records of less than 10 years are 0, and do not participate in snow classification statistics;

On the basis of quality control, count the average continuous snow days, snow period, snow days and snow fluctuation rate of each grid for many years;

The classification atlas of snow cover stability types in China from 1980 to 2020 is obtained;

Among them, 0.72 and 0.14 are the statistical median of R values of each grid in the range of continuous snow cover for more than 30 days and less than 10 days.