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Aims To investigate the eosinophil cell (EC) expression in peripheral blood of patients infected with severe acute respiratory syndrome coronavirus 2(SARS‐CoV‐2) and its clinical significance of diagnosis and prognosis. Methods 95 patients, whose nucleic acid test of SARS‐CoV‐2 was positive to make a definite diagnosis of COVID‐19, were selected as the study group. They were admitted at the Chengdu Public Health Clinical Medical Center from January 21 to March 2, 2020. Another 95 healthy subjects and 95 non‐infectious fever patients during the same period were selected as the control group. The BC‐6900 blood cell analyzer was used to continuously observe and detect ECs in 95 patients with COVID‐19 and the control group. The differences in expression levels of ECs in peripheral blood were analyzed. Results ECs were significantly decreased in 95 (75.8%) COVID‐19 patients (P < .01). The absolute EC count IQR was 0.01 × 10⁹/L (0 × 10⁹/L − 0.04 × 10⁹/L), and the EC percentage IQR was 0.3% (0.1% − 0.8%). As the patients’ condition improved, the ECs returned to normal, but for those without improvement, ECs continued to decline. Conclusions ECs decreased remarkably in patients with COVID‐19, and gradually returned to normal after the improvement of the patients’ condition, while EC continued to decrease in patients without improvement. It is suggested that ECs have certain clinical significance in the diagnosis and prognosis of COVID‐19, and may be a useful index in the early warning of acute infectious diseases.