Abstract: The heat-tolerance of the Chinese Holstein (52 herds high yield and heattolerance, together with 41 herds high yield and heat-sensitivity) was studied using RAPD-PCR ( 200 RAPD primers). The results indicated that the 581 bp (primer S441) and 680 bp (primer S463) fragments were found in heat-tolerance group. The homology between 581 bp fragment and KCNN2 gene got to 89%, as well as the homology between 680 bp fragment and NW_001024067.1|BtUn_WGA9442_2 got to 99%. According to its function it seems that the KCNN2 gene was a candidate of heattolerance gene. The 581 and 680 bp fragments were submitted to GenBank and the accession numbers of EF123743 and EF123744 were got, respectively. The ORF was not found in 581 bp fragment, however, 4 ORFs （ORF1, coding 48AA; ORF2, coding 34AA; ORF3, coding 45AA; ORF4, coding 34 AA）in 680 bp gene fragment were found. Using the sequence of RAPD-S441 and RAPD-S463, together with the SCAR primer designed by Premier 5.0 software, the RAPD-S441 marker (581 bp) was converted to SCAR marker.