This paper presents simulation analysis of load effects of bridges under random fleet. Based on actual data of vehicle loads on Guangzhou-Shenzhen Expressway and relevant statistical results, mid-span bending moments of long-span virtual simple-supported beams are calculated. Then probability distribution of the bending moments and extreme value distribution of the load effects within design reference period are obtained. Finally, characteristic values of mid-span bending moments and recommended values of design lane load are calculated, sequentially. The results studied in this paper can be as a reference for long-span bridge design, and also can be a reference for overloading control or weight charge policy.