The invention discloses a metal tungsten surface nanocrystallization device and a method thereof. The method comprises the following steps: taking a tungsten cylinder provided with small holes as a hollow cathode device to form a hollow cathode effect, ionizing helium gas to obtain low-voltage and high-current helium plasma, enabling the helium ions to carry out bombardment action on the surface of a tungsten sample, rapidly increasing the temperature of the sample to be higher than 1600K in 5 minutes through the hollow cathode effect, injecting a certain quantity of helium ions, then obtaining a nanostructure in tight connection with a matrix on the tungsten surface. According to the metal tungsten surface nanocrystallization device and the method thereof, the device is simple and convenient, is low in cost, simple in process and high in production efficiency, and is capable of forming uniform and consistent nanostructure growth layers in tight connection with the matrix on the surface of the metal tungsten; a new method for solving nanocrystallization of the tungsten surface is provided; the products can be further treated to obtain photocatalytic materials for preparing decomposition water.