Based on three bridge dismantlement, duct grouting density of prestressing tendons was investigated in-situ . The indices were analyzed statistically to find out the construction quality of PC box-girders in China. The investigation result indicated that the duct of prestressing tendons were only partially grouted, with over 50% ungrouted for longitudinal tendons and over 70% ungrouted for transverse tendons. Obviously, this increased the prestress loss in the tendons. The quantitative indices proposed in the paper is helpful in understanding the underlying reason for cracking and over flexing in the PC box girder ,and it also provided the important basis for structural analysis of PC box-girders.