Background: During the COVID-19 pandemic, the lack of warm, supportive, and positive relationships caused behavioral and psychological problems in children. This study aimed to predict the psychological well-being of primary school students during the COVID-19 pandemic based on parental self-efficacy and cognitive emotion regulation in mothers based on the mediating role of the parent-child relationship. Methods: The present applied research used a descriptive correlation in terms of data collection and analysis. This research was conducted on 385 cases, including students and their parents, who were selected using a random sampling method. The research instruments included the Reef's psychological well-being questionnaire (18 questions), Johnston and Mash parenting sense of competence scale, Garnefski's cognitive emotion regulation questionnaire, and Fine's parent-child relationship scale. Two psychology experts assessed the face validity of the questionnaires. Reliability of the questionnaires was measured using Cronbach’s alpha coefficients. SPSS software was used to analyze the data. Results: The average total scores of psychological well-being, parenting sense of competence, parent-child relationship, and cognitive emotion regulation were 68, 58.3, 72.1, and 61.4, respectively. Maternal cognitive emotion regulation was a significant predictor of the parent-child relationship (p< 0.01). We found that parenting sense of competence and maternal cognitive emotion regulation were able to predict students' psychological well-being through parent-child relationship during the COVID-19 pandemic. Conclusion: Increasing the level of parenting sense of competence and regulating parental emotions can improve the relationship between parents and their children.