Objective To explore the clinical and gene characteristics of Coffin-Siris syndrome caused by ARID 1 B mutation. Methods The clinical data and molecular genetic test results of Coffin-Siris syndrome caused by ARID 1 B gene mutation in a child were retrospectively analyzed, and the relevant literature was reviewed. Results A 2 -year- and 8 -month-old was brought to clinic for psychomotor retardation. He had difficulties in feeding and poor weight gain after birth. He presented a distinctive facial appearance including sparse scalp hair, low frontal hairline, arched shaggy eyebrows, long eyelashes, broad nasal tip, flat nasal bridge, thin upper lip, a thick and everted lower lip and thick lip hair. He had hypotonia and small toenails in right foot. A heterozygous missense mutation of c. 6257 T>C (p.Leu 2086 Pro) in ARID 1 B gene was found in the child by whole exome sequencing, which was not found in his parents and was a new variant. A total of 86 reported cases of Coffin-Siris syndrome caused by ARID1 B gene mutation were retrieved through literature search. The clinical characteristics of the patients were basically consistent with the reported cases. Conclusion Coffin-Siris syndrome is a rare autosomal dominant genetic disease that can involve multiple systems, and genetic testing can help diagnose.