This paper presents two new noise estimation methods in the orthogonal frequency division multiplexing system, which are based on the channel estimation. In the traditional noise estimation method, the noise power is achieved with subtracting the pilot signal power from the total received power. While the first new noise estimation method can get the noise power easily by the difference of the adjacent channels. The second new method is the modification of the first method. Compared with the traditional method, the two new methods are effective on the calculation complexity. Simulation results demonstrate that the estimation accuracy of the two new methods are better than the traditional method.