Abstract: The uncertainty sources of wedge load test of grade 10. 9 high strength large hexagon bolt with the diameter of 20 mm were analyzed, the influencing factors of bolt tensile strength were identified and the uncertainty of the test results was evaluated. The results show that the main sources of uncertainty of tensile strength in bolt wedge load test included test force value, bolt basic pitch diameter and minor diameter, test speed and rounding off of numerical value. The uncertainty of tensile strength was reported as R_m=1 114 MPa, U_rel=2%(k=2).