Background: There is a high prevalence of mental illness among healthcare students, and most students with mental health problems are reluctant to seek help from mental health professionals. Help-seeking is a component of mental health literacy (MHL). Although MHL is conceptualized as multi-dimensional, a theory-based multi-construct of MHL is still lacking. We aimed to build a theory-based multi-construct of MHL to explore the pathways of help-seeking. Methods: The data were obtained from a survey on MHL among healthcare students in 2018 (n = 1294). The Mental Health Literacy Scale for Healthcare Students was used to measure the maintenance of positive mental health, recognition of mental illness, mental illness stigma attitudes, help-seeking efficacy, and help-seeking attitudes. Descriptive analysis and structural equation modeling (SEM) were conducted. Results: The findings of the SEM model indicated recognition of mental illness had a positive direct effect on both help-seeking efficacy and maintenance of positive mental health. Additionally, help-seeking efficacy fully mediated the relationship between recognition of mental illness and help-seeking attitudes. Conclusions: Help-seeking efficacy plays a significant role in healthcare students’ willingness to seek professional help when mental health care is needed. Accordingly, improving help-seeking efficacy strategies would increase the use of mental health services and contribute to the prevention of mental health problems.