Disclosed are a material-saving type modular plastic formwork and a construction method thereof. The formwork comprises a panel. The outer side of the panel is sleeved with a surface skin which is a hollow sealed box body formed by connecting at least two parts in an inserting mode. According to the material-saving type modular plastic formwork and the construction method thereof, according to the functional needs in the application process of the formwork, the formwork is designed to be the panel part and the surface skin part, wherein the surface skin is a wearing part and is responsible for concrete forming quality control and protecting the panel, and the panel is a long-term used part and provides strong support for the formwork. The surface skin and the panel are supplementary to each other so that the number of times of service of the formwork can be increased by a large margin, the service life of the formwork can be prolonged by a large margin, and the problem of resource waste existing in the plastic formwork industry is solved. The surface skin is easy to repair and replace, can be repaired after damaged, and can be recycled and machined to be a new surface skin again if damaged badly, so that the environmental protection and energy saving effects are achieved, the number of times of service of the formwork can be increased by a large margin, and the service life of the formwork can be prolonged by a large margin. The material-saving type modular plastic formwork and the construction method thereof can be widely applied to a concrete pouring formwork system.