One of the problems in teaching English as a foreign language (EFL) is the teachers’ lack of knowledge on the process of the students’ text production, which seems to have not been adequately explored and described. This research aims to describe the process of encoding of Field in EFL learners' academic writing in English, especially argumentative texts, focusing on how students produce the texts and why they produce the texts as they do. A Mixed method is applied in this research; Qualitative data is collected from interviews and quantitative data is compiled from the texts produced by a group of 25 Indonesian university students, who become the subject of this research. The findings show that Indonesian students, when writing English argumentative texts, use mostly Material process, Relational process, and Mental process. Furthermore, the students mostly use Circumstance of Reason, Time and Circumstance of Degree. These types of Processes and Circumstances are encoded in the text for the reasons of elaborating, explaining, and expressing opinions, based on the question asked. In other words, the encoding of Field seems to be influenced by the question or prompt given. This has given an idea of how foreign language teaching should be conducted.