This longitudinal mixed-method study investigated effects of the reading-while-listening mode on the incidental learning of two dimensions of vocabulary knowledge, namely receptive knowledge and productive knowledge, in a Chinese EFL classroom context. Additionally, EFL learners' attitudes toward the reading-while-listening mode of incidental vocabulary learning were examined. Seventy-eight Chinese EFL students with typical vocabulary sizes around 2,000 from two intact classes at a senior high school participated in the study and assigned as the experimental and the control groups. Over a 10-week intervention, the experimental group engaged in incidental vocabulary learning through reading while listening, whereas the control group retained a traditional reading-only mode. The results from three vocabulary tests showed that the reading-while-listening mode was more effective for incidental vocabulary learning and retention than the traditional reading-only mode on the dimensions of sound recognition, meaning recognition, and meaning recall but not on the dimension of form recall. Questionnaire and interview data unveiled that Chinese EFL learners have positive attitudes toward reading while listening as a means of incidentally learning vocabulary. Through reading while listening, they developed learning interest, increased classroom engagement, improved learning efficiency, and built confidence in English learning. The study contributes empirical evidence supporting multimodal language learning approaches, offering practical recommendations for EFL instructional design and vocabulary learning strategies.