Abstract: Solar radiation is widely used in the studies of climate change, evaluation of model simulations and assessment of solar radiation energy resources. Therefore, accurate observations of solar radiation data are absolutely needed. An international BSRN method of solar data quality assessment and quality control (QA-QC) is applied to investigate data quality of solar radiation and downward long-wave radiation (DLR) measured from 2005 to 2011 at Lin'an and Longfengshan, two regional background stations in the mainland of China. The method includes 3 steps of testing. They are the sequential limits of physically possible, extremely rare and relevant factor comparison. The results show that percentages of radiation data meeting requirements of the first two test steps of the quality test at both sites are more than 99.5%, but in the third step, the percentage dropped to 97.9% at Lin'an and 95.9% at Longfengshan. The error of the 2AP (2 axis position) in tracking sun-disk is the main cause for those direct and diffuse radiation data failing to meet the conditions of quality test, and the scenario is more frequent at the high SZA (solar zenith angle). Compared to the rate evaluated by the prevalent limit of global radiation error, the BSRN third step makes the rate of validated solar radiation data be reduced by 0.9% and 1.6% at Lin'an and Longfengshan, respectively. The thermal offset of CM21 pyrometer is from-5 W·m^-2 to-2 W·m^-2. With the compensation of thermal offset, the rate of radiation data meeting requirements of the BSRN quality test is obviously improved.It is well known that the most important factor affecting the surface solar radiation includes cloud, water vapor and aerosol. Therefore, variations of solar radiation with changes of SZA are analyzed with removal of cloud effect. It is identified that the global and direct radiation irradiances at Lin'an are obviously lower than those at Longfengshan with the same SZA, while the diffuse radiation is opposite. The cause for these phenomena is due to the lower atmospheric transparency and higher atmospheric turbidity at Lin'an.The annual averages of solar radiation and DLR at the sites are calculated. The annual averaged daily integrated global solar radiation and global solar radiation under clear condition at Lin'an are 12.4±7.2, 16.5±5.0 MJ·m-2, while the coincident average radiations at Longfengshan are 13.5±7.2, 15.5±6.2 MJ·m^-2. Annual average DLR at Lin'an is 363.7±59.3 W·m^-2, obviously higher than that at Longfengshan (274.9±77.6 W·m^-2). There is an obvious decreasing trend of DLR at Lin'an, and global solar radiation takes on an increasing trend at Longfengshan under clear sky.