Provided is a base plate unit, which is of an integrated structure made of fiber reinforced polymer-matrix composite and comprises a base plate unit body and foot plates. The base plate unit body comprises at least one bearing part, each bearing part comprising a panel, a plurality of web plates extending downwards from the bottom of the panel, and bottom supports disposed at the lower end of the web plates. The web plates comprise two side-web plates on the two sides of the panel and a middle web plate in the middle. The foot plates are disposed on the two outer sides of the bottom of the base plate unit body, and are formed by the bottoms of the two side-web plates on the outmost side of the base plate unit body respectively extending outwards horizontally. Also provided is a base plate unit provided with a cavity filling member.