The invention aims at providing a metal powder fuel supply device based on overpressure sealing. A piston and transmission assembly driven by a motor is arranged at the upper end of a nanometer metal powder grain, and an annular nozzle is arranged at the edge of the piston and the transmission assembly. An annular gas collecting cavity is formed between a piston and the wall. A plurality of sealing rings are arranged between the annular gas collecting cavity and the external. An annular fluidization chamber is formed inside the piston and formed in the manner that an upper workpiece is connected with a lower workpiece through bolts. By means of the metal powder fuel supply device, the influences, caused when all metal powder is pushed by a piston for feeding and fluidization, on normal running and stable feeding of a system can be avoided; the difference between the gas pressure inside the annular nozzle and the gas pressure outside the annular nozzle forms overpressure sealing, and nanometer metal powder can not reflux to permeate upwards into the edge of the piston; due to a clean gap of the piston, the replacement frequency of the sealing rings is reduced, abrasion of the wall of the piston is reduced, and the environment is created for use of lubricating oil; and the nanometer metal powder is mainly used, and it can be avoided that metal particles are preheated and pre-burnt during fluidization to improve burning stability.