The research shows that although the number of questions in a class is uncertain, it is very important to accurately grasp the timing of questions. When and what questions to ask, the teacher must design them before class. If you can ask questions at the right time and temperature, it will have a very good effect; It can mobilize students' emotions, enliven the classroom atmosphere, ensure the quality of thinking and improve the teaching effect. It is also found that the opportunity to ask questions in class usually occurs in the following situations: first, when students know, feel and want to express their communication; Second, when students are suspicious, confused and want to ask questions; Third, when students' learning emotions need to be stimulated, regulated and expressed; The fourth is to promote students' self-awareness, self-evaluation and confidence multiplication. If teachers can accurately grasp the above questioning opportunities, the effectiveness of classroom questioning will be greatly improved.