Pi, the ratio of a circle's circumference to its diameter, is an important but irrational number in math. It is a frequently used number which can be used to find the circumference and area of a circle, as well as the surface area and volumes of spheres and cylinders. The purpose of this project to find pi with higher accuracy. A Java Monte Carlo simulation method is developed to generate random points in the coordinate. By counting the number of points inside and outside the circle, we can calculate the Pi. The sample size can be controlled in the Java program. For each sample size, it was repeated for twenty times see how the relationship between accuracy and the sample size. In the end, the Monte Carlo Method was revised to further improve the Pi accuracy.