Background <p>Nursing students face significant pressure due to academic burdens and clinical demands, which may increase their risk of mobile phone addiction. Mobile phone addiction impairs students’ psychosocial functioning and can lead to depression, anxiety, loneliness, inattention, and other adverse mental and physical health outcomes. This study addresses a critical gap in the literature by examining how stress perception, self-control, and psychological capital interact to influence mobile phone addiction among nursing undergraduates, a population uniquely exposed to high academic and emotional stressors. Understanding these factors is essential for designing effective interventions to reduce mobile phone addiction in this vulnerable group.</p> Methods <p>From September 2022 to November 2022, a stratified random sampling method was used to select 616 nursing undergraduates from a university in Shaanxi Province as the investigation objects. Subjective stress, self-control ability, mobile phone addiction tendency and psychological capital level of nursing undergraduates were evaluated by pressure perception scale, self-control scale, mobile phone addiction tendency and positive psychological capital questionnaire. The mediating effect was tested by percentile Bootstrap method with deviation correction, and the moderating effect was tested by PROCESS program.</p> Results <p>(1) Among the 592 valid questionnaires collected, 176 (29.72%) nursing undergraduates exhibited mobile phone addiction; (2) Self-control partially mediated the relationship between stress perception and mobile phone addiction tendency, with an effect value of 0.229, accounting for 59.02% of the total effect; (3) Psychological capital moderated the relationship between self-control and mobile phone addiction tendency, with the influence of self-control increasing as psychological capital levels rose (<i>β</i>= -0.099, <i>t</i> = -4.255, <i>p</i> &lt; 0.001).</p> Conclusions <p>This study highlights the novel role of psychological capital as a moderator in the relationship between self-control and mobile phone addiction among nursing undergraduates. The findings suggest that interventions aimed at enhancing self-control and fostering psychological capital could effectively reduce mobile phone addiction in this population. These results provide practical implications for nursing educators and mental health professionals, emphasizing the need for targeted stress management and resilience-building programs to support nursing students’ well-being.</p>