A reactor for thin film deposition and a thin film deposition method using the reactor are provided. The reactor includes: a reactor block which receives a wafer transferred through a wafer transfer slit; a wafer block which is installed in the reactor block to receive the wafer thereon; a top plate disposed to cover the reactor block; a shower head which is mounted on the bottom of the top plate and diffuses gas toward the wafer; and an exhaust unit which exhausts the gas from the reactor block. A first supply pipeline which supplies a first reactant gas and/or an inert gas to the wafer; a second supply pipeline which supplies a second reactant gas and/or an inert gas to the wafer; and a plasma generator which generates plasma between the wafer block and shower head are included. The shower head includes: a first supply path connected to the first supply pipeline; a plurality of first diffuse holes formed in the bottom of the shower head at a constant interval; a first main path formed parallel to the plane of the shower head and connecting the plurality of first diffuse holes and the first supply path; a second supply path connected to the second supply pipeline; a plurality of second diffuse holes formed in the bottom of the shower head at a constant interval as the plurality of the first diffuse holes; and a second main path formed parallel to the plane of the shower head at a different height from the second main path and connecting the plurality of second diffuse holes and the second supply path.