Hypocalcemia is a common condition in liver cirrhosis and is associated with the severity of SARS-CoV-2 infection. However, there is a lack of data demonstrating the prognostic value of hypocalcemia in COVID-19 patients with cirrhosis. This study aimed to evaluate the prognostic value of hypocalcemia for COVID-19 severity, mortality and its associations with abnormal liver function parameters. We selected 451 COVID-19 patients in this retrospective study and compared the laboratory findings of 52 COVID-19 patients with cirrhosis to those of 399 COVID-19 patients without cirrhosis. Laboratory tests measuring albumin-corrected total serum calcium were performed on admission, and the levels were monitored during hospitalization. The total serum calcium levels were significantly lower in cirrhosis cases (2.16 mmol/L) compared to those without cirrhosis (2.32 mmol/L). Multivariate analysis showed that hypocalcemia in COVID-19 patients with cirrhosis was a significant predictor of in-hospital mortality, with an OR of 4.871 (p< 0.05; 95% CI 1.566–15.146). ROC analysis showed the AUC value of total serum calcium was 0.818 (95% CI 0.683–0.953,p< 0.05), with a sensitivity of 88.3% and a specificity of 75%. The total serum calcium levels showed a significant negative correlation with the Child–Turcette–Pugh score (r = −0.400,p< 0.05). Hypocalcemia on admission was a significant prognostic factor of disease progression in COVID-19 patients with cirrhosis.