NOVELTY - The preparation method of tungsten trioxide nanoarray using one step hydrothermal process involves: UV treating the cleaned electrically conductive glass substrate; adding deionized water to 16M nitric acid; adding sodium tungstate dihydrate powder to deionized water; adding oxalic acid and ammonium sulfate to the sodium tungstate solution; adding the precursor solution to the glass substrate in autoclave lined with PTFE and performing hydrothermal synthesis reaction and cooling; washing the glass substrate with water and anhydrous ethanol and drying.    USE - Method is useful for preparing tungsten trioxide nanoarray, which is useful in solar cells and photocatalytic applications and for the preparation of an electrochromic film, a photochromic film and gas sensors.    ADVANTAGE - The method ensures simple, safe and economical preparation of the tungsten trioxide nanoarray with uniform morphology in controllable manner.    DETAILED DESCRIPTION - The preparation method of tungsten trioxide nanoarray using one step hydrothermal process involves: (a) cleaning an electrically conductive glass substrate to remove contamination layer on the substrate, UV treating the cleaned glass substrate using UV lamp for 15-30 minutes and drying in an oven at a temperature of 60 degrees C; (b) adding deionized water to 16 M nitric acid in a volume ratio of 1:1 to prepare nitric acid solution; (c) adding sodium tungstate dihydrate powder to deionized water to prepare sodium tungstate solution with a concentration of 0.023-0.024 mol/l; (d) dripping nitric acid solution into sodium tungstate solution to regulate the pH value to 1-1.5; (e) adding oxalic acid to sodium tungstate solution in a molar ratio of 1:10-1:40, adding ammonium sulfate to sodium tungstate solution in a molar ratio of 1:3-1:6 and then stirring to obtain final precursor solution; (f) arranging the electrically conductive glass substrate in an autoclave lined with PTFE; (g) adding the precursor solution to the autoclave and then performing hydrothermal synthesis reaction at a temperature of 180 degrees C for 8 hours and naturally cooling to room temperature; (h) repeatedly washing the electrically conductive glass substrate using deionized water and anhydrous ethanol and drying in an oven at a temperature of 60 degrees C.