A hollow-cathode plasma generator includes a plurality of hollow cathodes joined together and connected to a power supply for generating plasma in vacuum. Each of the hollow cathodes includes at least one fillister defined therein, a fin formed on a side of the fillister, an air-circulating tunnel in communication with the fillister and a coolant-circulating tunnel defined therein. The fillister is used to contain working gas. The fin receives negative voltage from the power supply for ionizing the working gas to generate the plasma and spread the plasma in a single direction. The working gas travels into the fillister from the air-circulating tunnel. The coolant-circulating tunnel is used to circulate coolant for cooling the hollow cathode.