The invention discloses a modularized decorative wall plate and an assembly method thereof. The modularized decorative wall plate comprises a wall body, a modularized whole, string courses, standard frames, vertical middle diaphragms, transverse middle diaphragms, a baseboard, clamping pieces, adjusting plates, an adjusting hanging plate and a top line. The modularized whole is arranged on the surface of the wall body. The standard frames are uniformly distributed on the modularized whole from the middle to the two sides. The vertical middle diaphragms are arranged at the left and right ends of the standard frames. The transverse middle diaphragms are arranged at the bottoms and the tops of the standard frames. A wall face vertical center line, a string course lower cornice auxiliary line and a baseboard upper cornice auxiliary line are drawn on the surface of the wall body. The clamping pieces, the baseboard, the vertical middle diaphragms, the transverse middle diaphragms, the standard frames, the adjusting plates, the adjusting hanging plate and the top line are all the fixed sizes, are in mutual fit and can produced on a large scale; the construction period is shortened greatly through the modularized assembly method; and the appearance of the wall surface is more attractive after decorating, and environmental protection is achieved.