Source evaluation is central to effective reading and decision making in digital environments. However, L2 students' processes of source evaluation and its role in task performance is not well understood. To fill the gap, the study examined 25 Chinese EFL undergraduates' online processes of source evaluation in an Internet environment. By analyzing data of pre-task interviews, screen-recordings, stimulated recalls and students' selected texts and written products, the study revealed four evaluation behaviours and six evaluation criteria that students engaged in. On average, students spent more time scanning search results and evaluated information and sources based on the criterion of determining relevance to the task more often. The follow-up Spearman correlation analysis showed that scanning search results was significantly and positively associated with the number of reliable texts, while the criteria of determining relevance to the task, examining source features and scrutinizing information accuracy were significantly and positively associated with total writing scores. Overall, the findings offer new insights into L2 students' source evaluation, with implications for curriculum designs, teaching practices, and task designs aimed at helping EFL students become more critical readers in the digital age.