The analysis of student situations is the beginning of teaching design. Since from the new curriculum reform, The teacher gradually realized that in order to enhance teaching effectiveness process they must pay attention to student situations. But in practical instructional design ，there still depend on subjective experience to carry on the problem of teaching design which is not clear for the analysis of student situations. In this paper, I take the example of The change of the length of day and night from the PEP geographic textbook（ Compulsory 1），the base is the guidance of teaching design in students' education practice. It illustrate the specific process in student situations. The paper has discussed the problems about how to ensure the effectiveness of classroom teaching and how to improve it according to student’s circumstances. The paper is aimed to provide scientific reference for geography teacher in carrying on the analysis of student situations.