To study the traffic characteristic and axles load spectra of a heavy load expressway, WIM data was collected, axle configuration and vehicles classification was determined. The characteristic of truck traffic monthly distribution and the truck hourly distribution was studied and axle load spectra for major tuck types were developed. The results show that there were more than 30 truck types running on the expressway, the peaks of truck traffic monthly distribution was in April, September and December and the rush hour of the hourly distribution was at midnight. All major axles had a bimodal pattern of load spectra. The second peak of single axle was about 12 to 13 ton, tandem axle 14 to 22 ton and the tridem axle 28 to 32 ton. More than 50% of axles were overloading.