Blackjack is a popular casino poker game in which players make drawing decisions based on rules other than the size of their points. We found that despite the randomness of the card draw, blackjack is actually very mathematical and logical. By calculating probabilities and using game theory, we can allow players to make relatively "rational" decisions that maximize their expectations of winning, rather than relying solely on guesswork and vague feelings. Therefore, in this article, we built several models to simulate a blackjack game with different numbers of people. For players in each model, we give them a code that outputs the optimal decision, which helps them figure out the winning percentage (more specifically, the expectation, since once stakes are involved in multiplayer games, the winning percentage doesn't necessarily represent the expectation of winning money) for each decision, thus helping the player make a better decision.