Ultra-low molecular weight polyethylene oxide (PEO) with viscosity-average molecular weight of less than 2.0×105 was obtained by molecular chain shearing under ultraviolet light with initial molecular weight of 1.5×106. The effects of ultraviolet wavelength, power, source distance, environmental tem-perature and humidity on the ultraviolet shear rate of PEO were studied. The structure and properties of PEO with different low molecular weight were characterized. The results show that ultra-low molecular weight PEO with viscous average molecular weight of 1.5×105、8×104、5×104 and 4×104 can be obtained in the test facility with the optimum reaction conditions with a UV wavelength of 185 nm, a power of 75 W, a light source distance of 5 cm, an ambient temperature of 35 C and a relative humidity of 20%. With the prolongation of shearing time, the molecular weight distribution coefficient of PEO decreases. The structure of PEO did not change significantly during ultraviolet shearing, only small amount of formate was formed. The melting point of PEO decreases and the crystallinity increases with the decrease of molecular weight.