Abstract: An ultraviolet radiometer (TUVR) by the Eppley Lab of the United States is among the most popular instruments used for its reasonable design. Although not being able to detect the overall ultraviolet radiation, irradiance at the frequency section between 385 nm and 400 nm could be measured. After some time since the instrument is first put into use at the institution affiliated with the authors, the irradiance readings are found to attenuate a little. Under normal circumstances, it has to be sent back to the manufacturer for calibration, which is unpractical and costly. Under existing regulations in this regard, the instrument is probably discarded. When spectrometers are not an option as they are inconvenient for field operation, two new instruments are then introduced as reference to determine the cause of errors and ways of correcting data received. For this purpose, experiments are designed and conducted to analyze quantitatively the error source and contribution of measurement of surface UV radiation using the ultraviolet radiometer. The result shows that the degradation of sensors and pollution in the teflon diffusing disk are the main error sources. The decreasing rate (y) of sensors decreases linearly with its exposure time (t) and the fitting curve in Guangzhou is y=0.66t. The measuring error from the diffusing disk is mainly related to air pollution. Although the transmission of cleaned disk will be changed, it has linear relation with that of the original diffusing disk, and the adherence to Lambert cosine law is not affected. The value corrected by factors is very close to that of standard radiometer, and the correlation coefficient approaches 1.0.