Abstract.Theory of Brownian motion is often used to describe the random phenomena of chaos and disorder. This paper tries to make an empirical study on the price of foreign exchange by using theory of Brownian motion. First of all, we use the theory to establish a model to describe the behavior of foreign currency prices.Then the data of the Euro against the US dollar, the Australian dollar against the US dollar and Gold against the US dollar closing price per hour is introduced to simulate the exchange rate by using the model. Finally, we will use the simulated price and the actual price to do a comparative analysis, including the error range, motion direction and inflection point. It was found that the simulation and the actual exchange rate very similar, the results show that this model can be used to forecast.