If you feel that you have a solid mathematical foundation, a good knowledge of functional topology statistics, and the ability to enter first-class academic groups, such as several national key disciplines of economics, or some well-known research groups such as Wu IAS of Central University of Finance and Economics, this is the best. The second best thing is to enter the economics major of a prestigious school, which is not difficult to achieve through hard work, and many teachers like to cross-test students majoring in mathematics. For example, econometrics can be considered. Moreover, as far as I know, the economic-related majors handed in have examination questions specifically for candidates majoring in mathematics, which seem to be examination letters or functionals. You can pay attention to them.

Besides, it's not bad to study math. Many schools have set up interdisciplinary directions such as financial mathematics, and it seems that the mathematics department of Shanghai Jiaotong University also has them. You can pay more attention to similar schools. I think I can take an examination of applied mathematics or probability theory and mathematical statistics in the master's stage. I have a classmate who majored in basic mathematics and studied economics with a doctorate, but everyone's situation is different. You should think it over.

I suggest that if you have the ability, you'd better apply for the economics-related major of a prestigious school directly. Mathematics is a tool. You can study mathematics while studying economics. This is not a conflict. However, if you want to be safe, you can apply for the math major. As long as you can pass the exam, you will always have the opportunity to contact and learn from the teachers of economics.