The invention discloses an electric propulsion testing platform gaseous-propellant supply device which consists of a high pressure gas cylinder, a gas cylinder manual valve, a gas cylinder pressure gauge, a discompressor, a discompressor valve, a discompressor pressure gauge, a metallic hose, a filter in front of a flow controller, the flow controller, a premixing cavity, a pressure sensor, a penetration front manual valve, a penetration flanged joint, an electromagnetic valve, a filter in front of an engine, a tee joint and a stainless steel canaliculus tubule. The gaseous-propellant supply device can propel gas which has single component in certain flow rate and pressure intensity, provides mixed gas propelling agent with certain mixing ratio, and has the advantages of stable work and accurate control of the flow rate.