The difference between simple diffusion and facilitated diffusion is that facilitated diffusion

Simple and facilitated diffusion are both similar types of phenomenon where the substances are moved from a region of high concentration to lower concentration across a semi-permeable membrane.

The main difference between them is that the facilitated diffusion requires a special type of protein or carrier molecules in order to transport the substances whereas simple diffusion does not require such molecules. The rate of flow of these substances is high in the facilitated diffusion in comparison to the simple diffusion.