ZnO nanorods are synthesised by the chemical solution method on indium tin oxide (ITO) substrate. The all-inorganic light emitting devices, with the structure of ITO/ZnO/ZnO nanorods/SiO2/Al, are obtained with various amount of SiO2 by different spin-coating speeds. According to energy dispersive spectrum (EDS) and absorption spectrum, the modification amount of SiO2 shows a gradual increase when the casting speed is reduced from 3000 r/min to 500 r/min. The electroluminescent (EL) spectra of devices, influenced by the casting speed, are measured and compared. For each spin coating speed, the EL intensity of devices shows obvious enhancement in the ultraviolet (UV) range with the applied voltage increasing ,whick is weakened simultaneously in visible region. The luminescent intensity in UV range enhances obviously when the casting speed increases to 1000 r/min and then declines gradually. At the same time, the visible emission disappears. The I-V curves reveal that the additional SiO2 modification drives up the turn-on voltage of the device monotonically and leads to a decline of maximum operating current. The discussion based on photolumine-scence (PL) spectra and the energy level diagram suggests that, besides surface passivation of ZnO nanorods by SiO2, the high barrier between ZnO and SiO2 induces electron accumulation and suppresses non-radiative recombination at ZnO layer. And the SiO2 on the surface of ZnO nanorods helps to improve the electron density and then the recombination rate at the higher levels of ZnO.