For the purpose of shaping terahertz Gaussian beam transmitted by the terahertz transmitter into a terahertz sheetlike flat-top beam，this article proposes a method of designing which combines a dual-phase plates with a terahertz lightsheet to shape beam. In theoretical design，we first use the input-output algorithm to design a dual-phase plates that can shape Gaussian beams into flat-top beam，and then shape the flat-top beam to a sheet-like flat- top beam through terahertz light-sheet. Numerical simulation was conducted and an experimental system was built at the same time of theoretical design. The results all indicate that the system can convert the Gaussian beam transmitted by 0.33 THz terahertz transmitter into a flat- top beam with a sheet-like distribution in space. The relative root mean square reaches 71.41% for the sheet-like flat-top beam obtained in this experiment which fully demonstrates the effectiveness of the design.