The invention discloses a thin-walled hollow pier diaphragm plate bottom formwork and a construction method thereof. A plurality of columns of vertical supporting plates (11) which are square blocks are evenly distributed in the middle inside a bottom formwork body (1), and fixing transverse rails (12) are arranged on the periphery inside the bottom formwork body (1), wherein a plurality of oblique supporting plates (121) which are square blocks are symmetrically arranged on the left sides and the right sides of the fixing transverse rails (12) on the bottom side; and PVC plastic pipes (5) arepre-embedded on a thin-walled hollow pier (3), threaded steel bars (4) are inserted into the thin-wall hollow pier, finally, the bottom formwork body (1) is placed on the thin-walled hollow pier (3),and thus mounting of the bottom formwork body (1) is completed. After concrete is poured into a diaphragm plate and reaches certain strength, bottom plate supporting steel bars for the diaphragm plate can be pulled out, and thus the purpose that the supporting steel bars can be reused so as to save steel is achieved.