The invention discloses a controllable preparation method of a niobium pentoxide nanosheet. The controllable preparation method includes the steps that S1, a niobate compound and a structure-directingagent are used for preparing a niobium oxide nanometer material; S2, the niobium pentoxide nanosheet is prepared. The prepared niobium pentoxide nanosheet is large in specific area and uniform in edge. According to the controllable preparation method of the niobium pentoxide nanosheet, the niobate compound is prepared into the niobium pentoxide nanosheet controllably under the effect of the structure-directing agent through a hydrothermal method, the specific area of the prepared niobium pentoxide nanosheet is increased, and the morphology and crystal form of the prepared niobium pentoxide nanosheet are improved.