The invention relates to a preparation method of spherical nanoscale niobium pentaoxide powder, comprising the following steps: niobium hydroxide and oxalic acid are heated and boiled in distilled water to prepare niobium oxalate solution; carbon black, the niobium oxalate solution and ethanediol are mixed according to proportion, the mass ratio of the niobium pentaoxide and the carbon black is 1:2-1:9, and the volume ratio of the niobium oxalate solution and the ethanediol is 1:2-1:3; pH value is adjusted to be 8-9 by ammonia water; the mixture is stirred, and the temperature is kept to be 60-70 DEG C for 8-15 minutes, and then cooling, water filling, placing still, filtering and drying are carried out; the dries product is calcined in a muffle furnace, so as to obtain the spherical nanoscale niobium pentaoxide powder. The prepared spherical nanoscale niobium pentaoxide powder has small grain diameter, particles are uniform and spherical and the dispersity is good; the purity of the product can reach more than 99.99 percent; the whole technological process is simple, the raw material source is wide, the price is low, the process is safe, and the method is beneficial to realizing industrialization.