[Purposes] The Moscow-Kazan High-Speed Railway is a key representative project at high latitude regions in which Chinese enterprises have participated. Therefore, it is necessary to understand the air temperature characteristics along the route to help the design and construction of this project. [Methods] Based on the monthly average air temperature dataset of CRU grid data from the Climate Research Unit (CRU) of the University of East Anglia (UEA) between 1901 and 2021, the variation trend and spatial variation characteristics of air temperature freezing and thawing index along Moscow-Kazan High-Speed Railway were studied. [Findings] In the Moscow-Kazan High-Speed Railway region, the average annual freezing index from 1901 to 2021 fluctuates between 411.23 ℃·d and 1 773.70 ℃·d and shows an overall decreasing trend. Simultaneously, the average annual thawing index during the same period fluctuates between 2 223.69 ℃·d and 3 170.31 ℃·d and exhibits an overall increasing trend. This indicates that the annual average air temperature along the Moscow-Kazan High-Speed Railway has been gradually increasing from 1901 to 2021. In terms of spatial distribution, the multi-year average freezing index in the Moscow-Kazan High-Speed Railway region demonstrates a clear increasing trend from west to east between 1901 and 2021. The multi-year average freezing index ranges from 841.55 ℃·d to 1 360.13 ℃·d. The multi-year average thawing index in the region shows relatively little variation overall, ranging from 2 654.40 ℃·d to 2 748.63 ℃·d, increasing slightly from the central region towards both the eastern and western sides. This suggests that from Nizhny Novgorod to Moscow, the air temperature gradually decreases, while from Nizhny Novgorod to Kazan, the air temperature gradually increases. The air temperature along the Moscow-Kazan High-Speed Railway is gradually rising from west to east. The warming trend is relatively less pronounced in the Moscow region, whereas the Kazan region stands out as the area with the most noticeable air temperature increase along this route. [Conclusions] Utilizing the air temperature dataset of CRU grid data to study the spatiotemporal variation characteristics of the air freezing and thawing index along the Moscow-Kazan High-Speed Railway is an effective means. It provides a scientific reference for researching climate change patterns, frozen soil conditions, and other engineering constructions along this route.