The invention belongs to the technical field of treatment of environment pollution, and more specifically relates to a modular system for purification of a polluted river water body and application of the same. The modular system mainly comprises a biological grating module, an elastic filling material adsorption bed module, a microbial ecological decomposition suspending bed module and a sunken plant ecological purification suspending bed module. The biological grating module is composed of a framework, sunken plants, floating plants and emerged plants; the elastic filling material module consists of a framework structure, hydrophilic elastic filling materials and hydrophobic elastic filling materials; the microbial bed module comprises a framework structure, a micropore aeration mechanism and microbes; and the sunken plant purification bed module is composed of the species group of sunken plants and a bed body. According to the invention, the position of the polluted river water purification modules in a water body can be adjusted according to pollution degrees of the water body; the modular system can effectively purify water quality of a polluted river water body and a black and odorous river water body and reduce river pollution load; therefore, the invention is of significance for purification of river water bodies.