When training beginners and advanced players, every tennis coach would ask the players to hit the ball with a lot of spin. He or she would stress the importance of spin of the ball. But just a few coaches would analyze why using spin would increase players' games with more aggressiveness and consistency. The principles of generating the spin of the ball and the impact of the Magnus effect to the ball will be discussed in detail in this article. And I'd also like to apply the principles to all kinds of tennis courts, creating more tennis strategy and tennis tactics for the players to defeat their opponents.