This is my first blog article. It is my research note. About the derivation of Diffusion Coefficient. Because in my school computer lab, there is no chinese input. So have to use english. I hope my work can do help others. Eistein ever derivated the coefficient. By Dr.Jaynes use Bayesian method to do the same thing, it looks much concise. If someone is of interest in this, please see the attachment. Derivation of Diffusion Coefficient By Dr.Jaynes