Background: China has experienced an outbreak of a novel human coronavirus (SARS-CoV-2) since December 2019, which quickly became a worldwide pandemic in early 2020. There is limited evidence on the mortality risk effect of pre-existing comorbidities for coronavirus disease 2019 (COVID-19), which has important implications for early treatment. Objective: Evaluate the risk of pre-existing comorbidities on COVID-19 mortality, and provide clinical suggestions accordingly. Method: This study used a nested case-control design. A total of 94 publicly reported deaths in locations outside of Hubei Province, China, between December 18 ^th , 2019 and March 8 ^th , 2020 were included as cases. Each case was matched with up to three controls, based on gender and age ± 1 year old (94 cases and 181 controls). The inverse probability weighted Cox proportional hazard model was performed. Results: History of comorbidities significantly increased the death risk of COVID-19: one additional pre-existing comorbidity led to an estimated 40% higher risk of death (p<0.001). The estimated mortality risk in patients with CHD was three times of those without CHD (p<0.001). The estimated 30-day survival probability for a profile patient with pre-existing CHD (65-year-old female with no other comorbidities) was 0.53 (95% CI [0.34-0.82]), while it was 0.85 (95% CI [0.79-0.91]) for those without CHD. Older age was also associated with increased death risk: every 5-year increase in age was associated with a 20% increased risk of mortality (p<0.001). Conclusion: Extra care and early medical intervention are needed for patients with pre-existing comorbidities, especially CHD.