Tungsten trioxides (WO3) nanorod arrays had been fabricated at different substrate temperatures by hot filament chemical vapor deposition. The morphology of the WO3 nanorod array is significantly dependent on the substrate temperature in a relatively narrow range (600-800 degrees C). Through the x-ray diffraction pattern, different preference growth directions of WO3 nanorods at different substrate temperatures were observed. A discussion of the possible growth mechanism is given. Furthermore, the substrate temperature during the growth was also found to be closely related with the morphologies of the nanorod arrays and their field emission properties.