[Objective] The desert plant Karelinia caspica exhibits extremely strong heat tolerance. Cloning and studying heat-tolerant genes from Karelinia caspica, and applying them to economically important crops such as cotton to enhance their heat tolerance, aims to provide a theoretical basis and genetic resources for molecular breeding of heat tolerance in crops.[Methods] Clone the KcPIF4 gene from Karelinia caspica and conduct bioinformatics analysis; Transient expression analysis in tobacco for subcellular localization of the protein; use qRT-PCR to analyze the expression levels of KcPIF4 in the roots, stems, and leaves of Karelinia caspica seedlings at 45°C for 5 min, 30 min, 120 min, and 240 min; observe phenotypic changes in Arabidopsis thaliana overexpressing KcPIF4 under 45°C treatment and measure related physiological and biochemical indicators. [Results] The full-length coding sequence of the KcPIF4 gene in Karelinia caspica is 1 593 bp, encoding 530 amino acids, with a conserved bHLH domain and differences in motifs compared to homologous proteins in various plants. The protein was localized on the guard cell membrane of leaf stomata. The qRT-PCR results indicate that the expression level of KcPIF4 in the leaves of Karelinia caspica initially increases, then decreases, and subsequently increases again with the extension of treatment time. At 240 minutes, the expression level is the highest, being 4.4 times higher compared to the control group. Arabidopsis plants overexpressing KcPIF4 under 45°C treatment showed less leaf yellowing and wilting compared to the wild type, with significantly higher levels of CAT, SOD, POD, chlorophyll a, chlorophyll b, and carotenoids, and significantly lower levels of MDA and relative conductivity compared to the wild-type. [Conclusion] The KcPIF4 exhibits a process of tolerance-response-adaptation to high temperature stress, enhancing Arabidopsis thaliana"s tolerance to high temperatures, indicating that this protein possesses heat tolerance.