Objective To analyze the clinical features, diagnosis and treatment and prognosis of hairy cell leukemia (HCL). Methods The clinical data of 11 HCL patients admitted to Fujian Medical University Union Hospital from Jan. 2016 to Feb. 2021 were collected and sorted out, and the clinical features, diagnosis and treatment effects and prognosis of HCL were analyzed. Results There were 7 males and 4 females, the median age at diagnosis was 57 (30-81) years old, and the median time from the onset of clinical symptoms or signs to diagnosis was 5.0 (0.5-26.0) months. At diagnosis, there were 6 cases with lymphoma B symptoms (fever, night sweating, and weight loss), 7 cases with infection (all pulmonary infection), and 3 cases with lymphadenopathy; all cases were accompanied by splenomegaly (3 cases of mild splenomegaly, 2 cases of moderate splenomegaly, and 6 cases of megasplenomegaly). All the 11 patients underwent first-or second-generation sequencing. The positive rate of B-Raf proto-oncogene, serine/threonine kinase V600E mutant type (BRAF^V600E) mutation was 81.82% (9/11); peripheral blood routine showed that the two lines decreased in 4 (36.36%) cases, the three lines decreased in 7 (63.64%) cases, and the monocyte decreased in 9 (81.82%) cases. Among the 11 patients, except 1 patient who received FC regimen (fludarabine 50 mg and cyclophosphamide 0.3 g for the first 3 d) and 1 patient who received R-CVP regimen (rituximab 500 mg for the first day; cyclophosphamide 1.1 g for the second day; vindesine 4 mg for the second day; dexamethasone 15 mg for the first 5 d) in the first course of treatment and changed to cladribine in the next course, the remaining 9 patients received cladribine monotherapy. One patient obtained complete remission after 1 course of treatment with FC regimen. Among the remaining 10 patients, 7 patients were treated with single course of cladribine and 3 patients were treated with 2 courses. Among them, 4 patients were treated with cladribine for 1-3 months, the curative effect was evaluated as partial remission, and the remaining 6 patients reached complete remission after 4-12 months of treatment. The overall response rate of 10 patients to cladribine was 100.00%. Ten of the 11 patients had adverse hematological reactions of grade 2-4 after cladribine treatment: 7 (63.64%, 7/11) cases had neutropenia, 6 (54.55%, 6/11) cases had thrombocytopenia, 4 (36.36%, 4/11) cases developed agranulocytosis with fever, and 3 (27.27%, 3/11) cases developed lung infection or upper respiratory tract infection. The patients with infection symptoms improved after anti-infection and supportive treatment. There were no other adverse reactions except hematological adverse reactions. The median follow-up time of 11 HCL patients was 14 (3-61) months, and the median overall survival and progression-free survival were not reached. During the followed-up, no patients had HCL disease progression, recurrence, or death. Conclusion HCL is a rare clinically indolent hematological tumor, which is sensitive to cladribine and has controllable adverse reactions. Patients with relapsed or refractory HCL can choose to enter clinical trials or consider joint use of other targeted inhibitors or monoclonal antibodies.