Objective:To explore the effect of health education based on theory of planned behavior combined with stepped care model on negative emotion, psychological flexibility and quality of life in patients with lung cancer undergoing chemotherapy.Methods:From October 2020 to December 2021, 108 chemotherapy patients who underwent lung cancer surgery in Affiliated Hospital of Weifang Medical College and had anxiety or depression that scores was greater than 7 in any dimension of the Hospital Anxiety and Depression Scale (HADS) were selected as the study subjects. The study subjects were divided into observation group ( n=46) and control group ( n=48) by random digits table method. Routine care was implemented in the control group. The observation group implemented health education based on the theory of planned behavior combined with stepped care model intervention. The HADS scale was used every 4 weeks to assess negative emotion in both groups. In observation, patients with negative emotion relief stop the next stage of nursing intervention, and patients without relief continue the next stage of higher intensity nursing intervention. Results:Before the intervention, there were no significant difference in the scores of negative emotion, psychological flexibility and quality of life between the two groups ( P>0.05). After intervention, the scores of all dimensions of negative emotion and the total score in the observation group were significantly lower than those in the control group, and the differences had statistical significance ( t=4.86, 3.19 and 4.53, all P<0.05). After the intervention the scores of psychological flexibility and quality of life dimensions and the total score in the observation group were higher than those in the control group, the differences had statistical significance (t values were -6.01--2.89, all P<0.05). After the intervention, there was no significant difference in the remission rate of negative emotions between the clinical observation stage of the observation group and the concurrent control group ( P>0.05). The remission rates of guided self-help, problem-solving therapy, psychological or drug therapy and total negative emotions in the observation group were 38.46%(15/39), 33.33%(8/24), 6/16 and 78.26%(36/46), respectively, which were higher than those in the control group, and the differences had statistical significance ( χ2 values were 7.04 - 13.80, all P<0.05). Conclusions:Health education based on the theory of planned behavior combined with stepped care model can effectively alleviate the negative emotions of lung cancer patients undergoing chemotherapy and improve psychological flexibility and quality of life.