This paper mainly studies the magnetic resonance imaging (MRI) denoising problem. In modern medicine, magnetic resonance imaging has become an important auxiliary tools for doctor to diagnosis and treatment of disease.There is a very important role of the denoising research in medicine. Most existing denoising method assumes that the noise variance is known, get rid of noise from the image directly. In fact, we don't know the real image noise variance. This article will be to estimate the noise figure of th...