Based on the continuous phenological observation data of 23 woody plant species in Hohhot from 1983 to 2014, the natural calendar was established, and the changes of main phenophases of natural calendar and phenological seasons since 1983 and the reasons for these changes were revealed by analyzing the differences of phenophases between 1983-1998 and 1999-2014 and the correlation between phenophases changes and climatic factors. The results showed that in comparison with those of 1983-1998 the start time of phenological spring(represented by the time of bud expansion of Salix babylonica) and summer (represented by the time of 50% of full flowering of Robinia pseudoacacia) in 1999-2014 was advanced by 7 days and 4 days separately; while the start time of phenological autumn (represented by the time of fruit drop of Sorbaria kirilowii) and winter(represented by the time of all leaves of Amygdalus triloba coloring) in 1999-2014 was delayed respectively by 3 days and 6 days. The order of phenophase in spring, autumn and winter changed in different degrees. Correlation analysis between the phenological index of the first date of a season and climatic factors preceding three months of the season indicated that the mean air temperature of the first preceding month showed negative correlation with phenological index of the first date of spring, and significantly negative correlation with that of summer, but a positive correlation with that of winter. Mean sunshine duration of the first preceding month was positively correlated with the phenological index of the first date of autumn but a negative correlation with that of winter, and mean rain capacity of the first preceding month was positively correlated with phenological index of the first date of summer. Additionally, the mean air temperature of the second preceding month correlated with the phenological index of the first date of summer negatively; while the mean rain capacity of the third preceding month correlated with that of the first date of autumn negatively. The raise of average temperature was probably the main reason for the changes of phenological season in Hohhot, and the average sunshine duration and average precipitation also affected the changes of phenological season in different extent.