Fatigue failure of high-strength bolts in pinned connection in large-span steel structure may occur due to cyclic loading. To study the fatigue property of the bolts,9 constant amplitude fatigue tests for the 12.9 grade M36 bolts with the material of 35CrMoA were carried out. S-N curves were fitted,the stress distribution of the bolts and the stress concentration factor were obtained based on numerical simulation. The fatigue failure mechanism was proposed through analyzing the graphs of high-strength bolt fatigue fracture. The conclusions are as follows：The stress concentration of the first thread root on the bearing surface and the point on the bolts where the connected plate crushes is serious，and the nominal stress concentration factor is 4.409. The destruct-ion of most bolts start from the point of sudden change of stress from numerical simulation. The characteristics of fatigue failure of the bolt specimens fracture are obvious. Furthermore，the fatigue life of specimens under different stress amplitudes can be reflected by the fitted S-N curves. The formulas for calculating the fatigue life under constant amplitude with nominal stress amplitude and notched stress amplitude as variables are obtained.By comparing the test results with the recommended values of allowable fatigue strength stipulated in the Code for Design of Steel Structures（GB 50017-2017），the corresponding nominal fatigue strength and notched fati-?gue strength of 2×106 times are 84.78% and 373.8% of the recommended value for component Z11 in the standard，while 42.39% and 186.9% of the recommended value for component J2.