〔Abstract〕 Genetic diagnosis and etiological analysis were performed on a patient with hypoxic-ischemic encephalopathy at birth. MRI technology was used to examine the brain of the child. G-band karyotype analysis technology was used to analyze the karyotype of the child and her parents. Chromosomal microarray analysis(CMA) was used to analyze the entire genome of the child and her parents for chromosomal copy number variation(CNV) and to identify the small supernumerary marker chromosomes. The results of MRI supported the diagnosis of hypoxic-ischemic encephalopathy of the child and found the appearance of Dandy-Walker malformation. Karyotype analysis showed that the mother's karyotype was 46, XX, t(10; 13)(p11. 1; q11)[11]/46, XX[19]. The karyotype of the father was normal. The karyotype of the child was 47, XX, + mar. The CMA results showed that there was no CNVs above 200 kb in the parents. The CMA results of the child showed that the chromosome 10 was repeated in p15. 3 p11. 1, and the fragment size was 38. 39 Mb. In conclusion, this study found a rare small supernumerary marker chromosome(sSMC) on chromosome 10. Its genetic pattern and pathogenicity were analyzed. It is considered that sSMC(10) is the cause of the patient.