To explore the relationship between thyroid hormone levels and suicide attempts, suicidal ideation, and clinical characteristics of patients with depression, providing a reference for clinical intervention. Methods: 1229 patients with depression who received treatment in Hefei Fourth People’s Hospital from January 2020 to July 2023 were recruited. Based on the medical history, 578 patients with suicidal thoughts and behaviors within the past month were included in the suicide attempt group (attempt group), 306 patients with suicidal thoughts without behaviors within the past month were included in the suicide ideation group (ideation group), and 345 patients without suicidal behaviors or thoughts within the past month were included in the no suicide behavior and ideation group (control group). We analyzed the baseline data of the three groups and the levels of thyroid hormones, as well as the correlations between the levels of thyroid hormones in the attempt group and ideation group and depressive clinical symptoms. Results: The HAMD cognitive impairment and hopelessness factor scores in the attempt group were significantly higher than those in the ideation group (both P<0.01), and the cognitive impairment factor score in the attempt group was higher than that in the control group (P<0.05). Among the three groups, the serum levels of T3, FT3, and FT4 were lower in the attempt group＜ideation group＜control group (all P<0.05), with serum T3, FT3, and FT4 levels in the attempt group being significantly lower than those in the control group (all P<0.05) serum FT3 level in the ideation group was significantly lower than that in the control group (P<0.05). Serum FT4 levels in both attempt and ideation groups correlated positively with the total scores on the HAMD and HAMA scales (P<0.05), while serum T3 and FT3 levels in the attempt group also correlated positively with the total scores on the HAMD scale (P<0.05). Logistic regression showed that FT3 levels and cognitive impairment factors in HAMD were independent risk factors for suicidal attempts among depressive patients (P<0.01), and FT3 levels and hopelessness factors in HAMD were independent risk factors for suicide ideation among depressive patients (P<0.01). Conclusion: There are significant differences in serum T3, FT3 and FT4 levels between patients with suicide attempts and ideation and those without. Serum FT4 levels in both the attempt and ideation groups correlated positively with the total scores on the HAMD and HAMA scales. Among depressive patients, serum FT3 level is an independent biological risk factor for suicide attempts and ideation, while cognitive impairment factor in HAMD score is an independent risk factor for suicide attempts, and hopelessness factor is an independent risk factor for suicidal ideation.