从抽屉原则、排列组合两个方面出发，分别阐述其知识基础，再结合具体实例分析其在数学竞赛中的应用，其中排列组合方面的例题又从三大类进行解析，分别是排列数和组合数的计算题、排列组合的应用题和排列组合知识在其他方面的应用。在解题过程中要注意关键性的“题眼”，挖掘题目隐藏的数学语言，将其题目本身与数学原理联系起来，恰当运用原理达到简洁快速解题的目标，激发青少年对数学的兴趣和热情，提升数学的乐趣。

Starting from the drawer principle and the permutation and combination , this paper elaborates their knowledge basis respectively, and then analyzes their applications in mathematical competitions with concrete examples. The examples of permutation and combination are analyzed from three categories, which are the calculation of permutation and combination, application questions about permutation and combination and the knowledge of permutation and combination in other applications. In the process of solving the problem, we can find the "key eyes" and dig up the mathematical language hidden in the title to link the problem with the mathematical principles, and apply appropriate usage of the principles to find the fast and simple solution method. By doing this, teenagers' interests and enthusiasm in mathematics can be aroused, the fun of mathematics will be promoted.