The invention discloses a preparation method of titanium dioxide nano powder, comprising the following steps: heating solid paraffin to a molten state, dropwise adding titanate into molten paraffin, fully and evenly stirring, cooling down to room temperature to obtain paraffin blocks dispersed with titanate, putting the paraffin blocks dispersed with titanate into water, heating and stirring, slowly releasing the titanate with the melting of paraffin, hydrolyzing the titanate in water medium to form dispersive and even emulsion, stewing, cooling and layering, taking out paraffin coagulums, centrifugalizing the solution, and calcining the obtained product in a retortfurnace to obtain the nano titanium dioxide powder. The method utilizes the solidification and melting of paraffin to controlthe whole reaction process, does not need to add any other organic surface active agent and dispersing agent, has the advantages of simple and easy control, green earth and repeated use of paraffin, and is particularly suitable for continuous production. The prepared product has high purity, even microcosmic appearance and size and good dispersity.