Flammulina velutipes ready-to-eat snacks are not commonly known. Response surface methodology was employed to optimize the process parameters in making ready-to-eat snacks. The optimum dehydration condition was found at a sucrose concentration of 30%, a vacuum pressure of −40 ± 1.5 kPa, an osmotic time of 165 s and a microwave intensity of 65 W/g. These parameters resulted in water loss, solid gain and sensory evaluation values of 39.15%, 6.96% and 7.87, respectively. The water diffusion rate and solid gain diffusion rate were 1.55 × 10−9 and 1.29 × 10−9 m2/s, respectively, when employing the optimum microwave vacuum osmotic dehydration (MVOD) parameters. When F. velutipes mushrooms were dried for 180 min by hot-air drying, the water content of the ready-to-eat snack was 9.8 ± 0.5% and the water diffusion rate was 1.14 × 10−11 m2/s. Both the MVOD and the hot-air drying stages were consistent with the Page model.