本文是蒙特卡罗方法在数学上的一个简单应用。利用蒙特卡罗方法将确定的数学问题变成概率问题，并随机抽样，根据抽样结果，计算出单位圆的面积。-This is the Monte Carlo method in a simple mathematical applications. Using Monte Carlo method to determine the problem into mathematical probability and random sampling, the sample results to calculate the size of the unit circle.