This study aimed to interpret and describe students' mathematical thinking processes of non-routine mathematical problems that were solved based on didactic situation theory. This study uses a qualitative method, a phenomenological hermeneutics study for grade 8 students at a junior high school in Banda Aceh in the 2021-2022 academic year. Research data obtained through data were collected using instruments, namely written tests based on the didactic mathematical situation theory framework, structured observation, documentation, and clinical interviews carried out after the action. The results of the study show that the students' mathematical thinking processes in the critical reflection category can reach the convincing stage with algebraic arguments in validation situations. Subjects in the explicit reflection category can reach the convincing stage by providing arithmetic arguments in validation situations. Meanwhile, the category of students who cannot solve problems and can only specialize by giving examples of what is being asked. Students in this category have difficulty identifying relevant patterns and formulating the mathematical models needed to solve the problems. To support students in developing the level of mathematical thinking, the teacher can present contextual problems that are in accordance with the level of student thinking, can predict possible responses or ways of thinking of students to the problems given and present problems according to the structure of the concept sequence and the functional order of students' thinking. To support students in algebraic thinking category, teachers can start learning by presenting contextual problems that are easily recognized by students, then expand that context in symbolic form.