Abstract: The variations of PAR and VIS were analyzed, in terms of the observation data of solar radiation (photosynthetically active radiation (PAR), visible radiation (VIS), global radiation (Q), and etc.) and meteorological factors from four stations in North China from September 2004 to October 2006. The results show that the ratios of hourly sums of PAR/Q, VIS /Q and PAR/VIS are relatively stable. The diurnal, daily and seasonal variations of them are obvious, which are influenced by water vapor, scattering factor, cloud, and etc. The averages of hourly VIS/Q, PAR/Q and PAR/VIS in Yucheng, Luancheng, Xianghe and Xinglong from 2004 to 2006 are 0.39, 1.95 mol/MJ, 4.97 mol/MJ; 0.39, 1.94 mol/MJ, 4.95 mol/MJ; 0.43, 2.16 mol/MJ, 4.97 mol/MJ; 0.42, 2.03 mol/MJ, 4.89 mol/MJ. The empirical formulae calculating hourly sums of PAR and VIS under weather conditions in North China and conversion formulae between PAR and VIS are established. The calculated values of PAR and VIS are in good agreement with the measured, and their relative biases are 13.0% and 12.4%, respectively, if water vapor and scattering factor are both considered. Considering the limitation of direct or scattering radiations at some stations, only water vapor factor can be selected, so the relative biases between the calculated and the observed are 13.2% and 12.8%, respectively. Water vapor is an important factor controling the transmission and the simulation of PAR and VIS. At the same time, the scattering factors are also important.