The invention belongs to energy chemical technical field, especially relates to a fluidized bed reactor and a method for preparation of polyoxymethylene dimethyl ethers from dimethoxymethane and paraformaldehyde. The fluidized bed reactor comprises a gas inlet, a gas distributor, a catalyst inlet, a gas outlet, a fluid inlet, a catalyst outlet, a bottom component and an interstage component, a bottom component related gas upward channel, an interstage component related gas upward channel, a fluid outlet, a bottom downcorner and an interstage downcorner. A process for preparation of polyoxymethylene dimethyl ethers comprises the steps of: fluidizing gas is introduced into a bottom bed from the gas inlet via the bottom component related gas upward channel through the gas distributor; the fluidizing gas goes upwards and flows out of the reactor via the gas outlet; paraformaldehyde and dimethoxymethane are introduced into a bed through the fluid inlet; the fluid goes downwards and leaves the reactor via the fluid outlet. Compared with a conventional cannula reactor, the fluidized bed reactor improves the dispersion uniformity of catalyst and conversion of formaldehyde.