The invention relates to a method for synthesizing niobate sheet-shaped formwork powder. The method comprises the following steps: (1) preparing niobate precursor solution; (2) placing the niobate precursor solution in a high-pressure reaction container, reacting for 1-24 h at 30-200 DEG C, performing cooling and filtration, washing and drying a precipitated product, and obtaining the niobate sheet-shaped formwork powder. According to the synthesizing method, niobate crystalline hydrate is obtained through hydrothermal synthesis at the temperature lower than the temperature for conventional hydrothermal reaction (even at the ultralow temperature close to room temperature) and serves as the formwork powder and is introduced to the field of lead-free piezoelectric materials. Due to the fact that the niobate sheet-shaped formwork powder is simple, clean and environmentally friendly in the manufacturing process, the experimental cost is effectively reduced, and the mass production is facilitated.