Fatigue tests of bolted joint were carried out under constant amplitude loading. In all tests, bolts were broken at the root of the first thread where the nut and bolt were engaged. The relationship between the stress amplitude, which was defined as the load divided by the effective cross-sectional area of the bolt, and the number of cycles to failure showed a curve similar to a typical S-N curve. To estimate the axial force of bolt in bolted joint, the compressive force of bolted joint was detected by using the self-made load cell during the fatigue test. The maximum compressive force decreased as the cycle increased, while the minimum compressive force was equal to zero independent upon the load cycle. The axial loading pattern applied to the bolt could be estimated based on the change of maximum compressive force and the test load amplitude. The fatigue tests of bolt were carried out under the estimated loading pattern. The fatigue life of bolt was in good agreement with the life of bolted joint.