This study aimed to evaluate the atypical lymphocyte warnings of Sysmex XE-4000 in outpatient children. [Method] Randomly 280 specimens of outpatient children were selected to analyze atypical lymphocytes with Sysmex XE-4000 and artificial smear microscopy simultaneously. [Result] With artificial smear microscopy as the gold standard, the atypical lymphocyte warnings of Sysmex XE-4000 in outpatient children exhibited a sensitivity of 97.4%, specificity of 69.3%, positive predictive value (PPV) of 55%, and negative predictive value (NPV) of 98.5%. [Conclusion] Sysmex XE-4000 shows a high sensitivity in atypical lymphocyte warnings, which can reduce the number of blood smears, improve the specificity of microscopy, and decline the labor intensity of inspection personnel. However, there are stil certain false positives to be confirmed by artificial microscopy.