The invention discloses a gas supply device and a plasma reaction unit thereof. The gas supply device comprises a reaction gas source connected with a gas storer through a first control valve, and the gas storer is connected with a pressure measuring device and conveys reaction gas into a vacuum reaction cavity through a second control valve. As the gas storer with a fixed volume is adopted, the flow of gas entering the reaction cavity can be controlled conveniently and accurately by monitoring pressure intensity in the gas storer, the gas storer can be inflated and deflated fast by using the control valves, and the problems that in the traditional technology, as a mass flow controller (MFC) is adopted, gas switching speed does not meet the requirement, the state of a scallop-shaped rough surface on a silicon through hole side wall is poor, and when radio-frequency power is pulse output, the reaction gas is wasted are solved.