A vapor deposition reactor includes a chamber filled with a first material, and at least one reaction module in the chamber. The reaction module may be configured to make a substrate pass the reaction module through a relative motion between the substrate and the reaction module. The reaction module may include an injection unit for injecting a second material to the substrate. A method for forming thin film includes positioning a substrate in a chamber, filling a first material in the chamber, moving the substrate relative to a reaction module in the chamber, and injecting a second material to the substrate while the substrate passes the reaction module.