While research on informal digital learning of English (IDLE) has proliferated recently, there still exists a noticeable gap in factors that influence language teachers' attitudes and intentions to incorporate IDLE into the formal curriculum context. To address this gap, this study drew on the theory of planned behavior (TPB) and collected questionnaire responses from 1008 English language teachers in the Chinese mainland context. A structural equation modeling (SEM) approach was utilized to construct a hypothesized structural model and analyze the quantitative data. By validating the TPB-supported structural model, the findings showed that language teachers' behavioral intention to embrace IDLE in the classroom was positively and strongly predicted by their Attitude, Subjective norm, and Perceived behavioral control. The SEM also revealed external variables that could account for the formulation of teachers’ Attitude, Subjective norm, and Perceived behavioral control respectively. In addition, the results of two-group difference tests displayed that in-service teaching experience served as a significant moderator in the three paths from Subjective norm to Behavioral intention, Perceived behavioral control to Behavioral intention, and Control beliefs to Attitude. Finally, this study proposes implications for future research and practices based on the discussion of these results.