Identifying and studying freezing level is an important issue in aviation weather science. Due to the global warming climate, the altitude of freezing level, especially in the subtropical, is increasing, which has attracted the attention of many meteorological and climatological researchers, and many studies have been conducted in this field. To quantify these changes, it is necessary to statistically study the changes in freezing level elevation due to climate change and global warming. In this study, in order to identify the freezing level at each point, temperature information was used at different levels of the atmosphere above that point. The oldest and most common method for determining freezing level is the use of radio-sounding data, and this method is performed twice a day at 00 and 12 UTC. Therefore, due to the dispersion of this data in the period under study (if available), this information was collected at three stations of Mehrabad, Mashhad, and Kermanshah airports. Analysis of freezing level changes in selected airports of the country, in different months, seasons, and years using the Mann-Kendall test, does not show an upward or downward trend. In other words, monthly and seasonal changes in the height of this level in different years are not dependent on climate change. Synoptic investigating indicate that changes in the altitude of the freezing level at different years depend on atmospheric systems and the synoptic conditions of the studied month or season.