The invention relates to a preparation method of a tungsten bronze nanosheet. The preparation method comprises the following steps: (1) weighing tungstate according to a chemical stoichiometric ratio and preparation amount of MxWO3 (wherein M represents at least one or two of Li, Na, K, Rb or Cs), and weighing organic acid according to a molar ratio of tungsten in tungstate to carboxyl in organic acid, namely 1 to 3; (2) carrying out ball milling on reactants weighed in the step (1) for 0.5-6 hours, drying, and carrying out ball milling; (3) taking out a product obtained in the step (2), washing, filtering, and drying; (4) weighing an alkali metal source matter according to the chemical stoichiometric ratio and preparation amount of MxWO3, carrying out ball milling on the alkali metal source matter and a product obtained in the step (3) for 1-6 hours, and carrying out thermal reduction in a reduction furnace; and (5) washing, filtering and drying a product obtained in the step (4), so as to obtain the tungsten bronze nanosheet. The preparation method has the characteristics of simple equipment, high yield, no additive, environment friendliness and low cost.