To study the communication performance of non-line-of-sight (NLOS) ultraviolet (UV) communication in foggy environments, we propose a new attenuation model and a simplified calculation method of asymmetric factors. These solve the problems that the common fog attenuation model is not suitable for ultraviolet atmospheric channel attenuation and the calculation of multiple scattering transmission model is complex. A single-input-multiple-output (SIMO) ultraviolet communication system is established using the diversity receiving technology. First, a UV attenuation model is developed based on the Mie scattering theory to calculate the UV attenuation parameters of two fog types at different concentrations. Second, the asymmetric factor of a droplet size is established to simplify the calculation. Finally, the equal-gain combining technique is used to combine the diversity received signals. The performance of the SIMO UV communication system is analyzed by the Monte Carlo method and compared with that of the SISO UV communication system. The results show that diversity reception can effectively improve the performance of ultraviolet communication on foggy days: on thick, medium and thin fog days, and the maximum communication distance of the SIMO communication system is about 5, 10, and 10 m longer than that of a SISO communication system, respectively. When the bit error rate of the SISO ultraviolet communication system is 10^-3, the bit error rate of the SIMO communication system is reduced to about 10^-5.