Objective To explore the effects of treatment decision aid on addressing decision-making difficulties and anxiety, depression in patients. Methods Totally 289 patients with lung cancer who were treated in Harbin Medical University Tumor Hospital between July and December 2016 were selected by purposive sampling and randomly divided into treatment group (n=147) and control group (n=142). Patients in the control group received routine guidance and health education from doctors, while patients in the treatment group received decision support manuals and took part in treatment decision-making with medical staff. The Decision Distress Scale and the Hospital Anxiety and Depression Scale were used to assess the intervention effects. Results There was no statistically significant difference between the two groups judging from the scores of the Decision Distress Scale before the intervention (t=0.237, P=0.532). After the intervention, the patients in the treatment group scored lower than the patients in the control group (t=6.437, P<0.001), and there was no statistically significant difference in the level of anxiety (t=0.214, P=0.617) and the level of depression (t=0.105, P=0.874) between the two groups. Conclusions Treatment decision aid can address the decision-making distress and mitigate the sense of uncertainty in patients effectively.