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The β-ketoacyl CoA synthase encoded by the <i>KCS</i> genes is a rate-limiting enzyme for the synthesis of very-long-chain fatty acid (VLCFA), which catalyzes the VLCFA elongation. Yellow horn (<i>Xanthoceras sorbifolium</i>) is a horticultural tree species known for its kernel oil, which has strong resistance to drought, cold, high temperature, and saline-alkali. The conserved domain FAE1-CUT1-RPPA and ACP-syn-III_C of the KCS gene family were used to search the <i>KCS</i> sequences across the whole genomic sequence of yellow horn; a total of 20 <i>XsKCS</i> genes were identified and divided into four subfamilies. The conserved motif and transmembrane structure analysis revealed that most XsKCSs had a conserved transmembrane domain except XsKCS10 and XsKCS20. The prediction of cis-acting elements of <i>XsKCS</i> genes showed that <i>XsKCS</i> genes contained many stress and hormone response elements, such as ABRE, MBS, and LTR. Furthermore, <i>XsKCS</i> genes exhibited differential expression profiles under abiotic stress and stress-related hormone treatment conditions. Transcriptomic data showed that <i>XsKCS1</i>, <i>XsKCS11,</i> and <i>XsKCS17</i> had higher expression in yellow horn with high leaf cuticular wax, indicating that they may function in the cuticular wax accumulation and drought response. This study laid a foundation for further functional verification of XsKCS genes in yellow horn stress response.