Objective To explore the gene diagnosis of Gitelman syndrome. Methods The clinical data of a child with Gitelman syndrome were retrospectively analyzed along with gene detection results of his elder sister and parents. Results A 6-year-old boy was hospitalized for fever and hypokalemia. Gene detection of SLC12A found a new locus mutation of EXON21 c.2522A>G p.(Asp841Gly) and a heterozygosis of EXON16 c.1946C>T p.(Thr649Met). The diagnosis of Gitelman syndrome was confirmed. His mother carried a heterozygosis mutation of EXON21 c.2522A>G p.(Asp841Gly), while his father and elder sister carried a heterozygosis mutation of EXON16 c.1946C>T p.(Thr649Met). Conclusion Gene detection of SLC12A is helpful in the diagnosis of Gitelman syndrome. The newly discovered mutation of SLC12A3 gene has enriched the mutation spectrum of Gitelman syndrome.