Objective To evaluate the influence of thyroid hormone levels on prognosis of the patients with community-acquired pneumonia(CAP). Methods A total of 343 CAP patients admitted to the Emergency Department of Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine from January 2018 to October 2020 were enrolled in this study. The clinical data of patients, including gender, age, basic diseases, thyroid hormone levels [total 3, 5, 3’triiodothyronine (TT₃), total thyroxine (TT₄), free T₃ (FT₃), free T₄ (FT₄), thyroid stimulating hormone (TSH), reverse T₃ (rT₃)] and serum albumin, white blood cell (WBC）, procalcitonin (PCT), C-reactive protein (CRP), D-dimer, pneumonia severity index (PSI) scores and CURB-65 scores were collected. According to the prognosis, they were divided into survival group (n=321) and death group(n=22). The relation between the factors mentioned above and prognosis was analyzed. Results The levels of TT₃, TT₄, rT₃, TSH and serum albumin in the death group were lower than those in the survival group (all P<0.05), while the levels of D-dimer, PSI scores and CURB-65 scores in the death group were higher than those in the survival group (all P<0.001). There was no significant difference in the levels of FT₃, FT₄, PCT, CRP and WBC between two groups (all P>0.05). The average age of death group was higher than that of survival group (80.55±7.80 vs 73.66±13.57, P=0.019). Univariate Logistic regression analysis showed that TT₃ ( β=-3.389) was the best predictor of CAP mortality, which was higher than serum albumin level ( β=-0.213), D-dimer ( β=0.909), PSI scores ( β=0.027) and CURB-65 scores (β=0.597). Multivariate logistic regression analysis showed that TT₃ was independently associated with mortality in patients with CAP, and negatively correlated with PSI scores (r=-0.489, P<0.001), CURB-65 scores (r=-0.474, P<0.001), age (r=-0.344, P<0.001), D-dimer (r=-0.374, P<0.001), and positively correlated with albumin (r=0.353, P<0.001). Conclusions Thyroid hormone levels, age, serum albumin, D-dimer, PSI scores and CURB-65 scores were related to the prognosis of CAP. TT₃ was an independent predictor of the prognosis of CAP among all thyroid hormone indicators, and TT₃ combined with PSI scores, or CURB-65 scores can improve the efficacy to predict CAP outcome.