A linear-type microwave-excited plasma source mainly comprises a reacting chamber, a rectangular waveguide and a linear biased slot in between. A linear quartz plate with an o-ring embedded in the biased slot is required so as to keep the reaction chamber in low pressure condition. Plasma will be excited in the reacting chamber by microwave powers radiating from the biased slot. A linear-type movable dielectric material can be disposed in the waveguide to control the radiation intensity of microwave, such that the length of the linear-type plasma source is able be extended without increasing input microwave powers and thus large-area low-cost plasma-processing applications can be implemented.