1. Economics is a big subject, and most subjects don't need mathematics. But there are also a lot of mathematical needs, such as econometrics and games, all of which are mathematical modeling. What level of mathematics you need to study economics depends on what you study. Economics does not require a high level of mathematics, but also depends on what you want to learn. If you only study economics in general, you can have a preliminary understanding of calculus, linear algebra and probability theory.
2. For the intermediate level of economic knowledge, you don't need too advanced mathematical knowledge. Just master simple calculus. If you want to track some frontier fields, the requirements for mathematical knowledge are higher at this time. At this time, the relationship between economics and mathematics is somewhat similar to that between physics and economics. Generally speaking, if you master the basic knowledge of measurement, you can know what kind of story the author is telling. Basic mathematical analysis, functional analysis, random function and mathematical statistics are still needed.
3. To learn econometrics, the game should at least reach the level of knowledge mastered by mathematics undergraduates in the first two years. If you want to understand the cutting-edge academic articles, you must learn: mathematical analysis, advanced algebra, mathematical statistics, functional analysis, and modern probability theory. You don't need to learn too deeply, but you must master the great theorem and proposition skillfully. Many economists study mathematics at first.
4. Mathematical knowledge needed by undergraduates majoring in economics: calculus; Linear algebra; Multivariable calculus; Real analysis; Probability theory; Mathematical statistics; Game theory; Differential equation.