The performance of optical wireless communication systems (Radio-over-Fiber, ROF) will be reduced by noise interference, such as shot noise and relative intensity noise. In order to improve the performance of optical fiber ROF, a method based on variance normalization transform is proposed to realize the normalized noise power. First, a more accurate noise model is used to analyze the ROF channel, so as to better analyze the noise related to the signal. Then, the noise related ROF channel is transformed into a signal additive Gauss white noise channel, which is suitable for common signal transmission technology. The experimental results show that the proposed method can significantly improve the performance of ROF in terms of signal to noise ratio.