With the rapid development of information technologies, informal digital learning of English has emerged as an innovative computer-assisted language learning method. This study aims to examine the variables influencing informal digital English learning through a structural equation model since no studies have been devoted to this topic. Through data collected from a comprehensive questionnaire (n = 1047) and the structural equation model through AMOS 24.0, this study concludes: (1) The informal digital English learning activities, learners' grit, self-confidence, feedback handling skills, and interest enhancement positively and significantly predict willingness to communicate in informal digital English learning contexts significant at p = 0.05; (2) Willingness to communicate negatively and significantly predicts vocabulary knowledge scores in informal digital English learning contexts at p = 0.05; (3) Gender, age, and major significantly moderate the relationships between constructs in informal digital English learning contexts at p = 0.05, which is considered to have filled a research gap in informal digital English learning contexts. Future research directions are suggested.