This research focuses on the change rules of solar radiation effects and the relationship between most unfavorable live load effect and temperature effect of suspension bridges under natural environment. The fine model of an under-construction long-span suspension bridge was established, the parameter sensitivity analysis of environmental factors of solar radiation effects was carried out, and the relationship between the solar radiation effects and the most unfavorable live load effect was investigated. Results showed that the solar radiation effects of suspension bridge were mainly affected by ambient temperature, followed by the wind speed, the influence of which is nonlinear. Daily ordinal number and latitude had little influence on the solar radiation effects. The change of solar radiation effects was not consistent with that of latitude, but was affected by many environmental factors. The maximum deflection of the main beam caused by the most unfavorable live load was twice the maximum deflection caused by thermal radiation, and the offset of the tower top was equal to that of thermal radiation. These results could provide theoretical basis and technical support for the error analysis of the construction phase of suspension bridges and eliminate the temperature influence of the health monitoring data.