Abstract The thesis is mainly about complex numbers and geometric definitions included in senior high school math textbooks. The first half of the thesis, from chapter 1 to chapter7, is based on senior high school math textbooks and materials on the Internet. On top of that, my perspective and interpretation is supposed to make it easier to understand complex numbers and geometric definitions. The contribution of the thesis mainly lies in the second half, ranging from chapter 8 to 10. Chapter 8 is intended to clarify the concepts of geometric definitions of complex numbers, which hopefully helps students to cope with the confusing parts. In chapter 9, basic practice questions are provided to equip students with basic concepts. By practicing the basic questions, students are supposed to get familiar the concepts. Meanwhile, in chapter 10, more complicated questions are provided for more advanced students, who are expected to solve the questions based on the concepts they have learned previously.