Teaching writing for EFL students faces many interesting and challenging factors regarding students' and teachers' factors such as learning style, teacher's role, and teacher's teaching method, so that, every English teacher is suggested to choose an appropriate teaching method to maximize student's ability in producing a good writing. Based on the phenomenon above, joint construction, as the model of teaching writing is selected to be investigated in this research that is grounded by genre-based approach. This research aims to describe the undergoing process of students learning to write through the process of joint construction toward students' writing skill. The participant of this research is a senior English teacher since she has got many experiences in teaching process. This research used qualitative inquiry that employs model of phasal analysis (Gregory, 1985;1988;Dreyfus, Macnaught & Humphrey, 2011) as design to analyze the different stages of joint constructions. Therefore, the data of this study is drawn by observation and documentation of students' writing. The findings of this research showed that joint construction had been well implemented by the teacher in the classroom. The findings also pointed that joint construction helped students to manage and develop their ideas in constructing a text. Although joint construction gave a good effect of students written text length, it does not give effect of students written text quality.