The aims of this study were to investigate the effects of a positive psychological intervention on the mental health and happiness of patients undergoing In vitro fertilization (IVF), and to observe the pregnancy outcome of the IVF patients. Two hundred infertile women requiring IVF were randomly divided into an intervention group (Group I) and a control group (Group C), with 100 patients in each group. Both groups were given routine treatment and IVF nursing. Group I was further provided with a positive psychological intervention. The Symptom Checklist-90 (SCL-90) and Memorial University of Newfoundland Scale of Happiness were used to evaluate the mental health and happiness of patients. The difference in the pregnancy outcome between the two groups was also observed. The total SCL-90 score, total average score, number of positive items, interpersonal sensitivity score, depression score, and anxiety score in Group I were significantly lower than in Group C (P<0.05). The total happiness score, positive affect score, and positive experience score in Group I were significantly higher than in Group C (P<0.01), whereas the negative affect score and negative experience score in Group I were significantly lower than in Group C (P<0.01). Thus, a positive psychological intervention can improve the mental health and happiness of patients undergoing IVF, and improve the clinical pregnancy rate.