The completely overlap joints used in an eccentric offshore jacket were investigated by both the experimental method and finite element analysis. A full scale specimen was tested under cyclic quasi-static loadings to understand its performance under seismic loading. In the test, local buckling was first observed at the through brace in the intersection area. Then, a crack was found in the weld toe between the lap brace and the through brace. The propagation of the crack led to final failure of the joint. Some indicators to assess the performance of the joint were evaluated within the context of seismic resistance. The energy analysis indicated that the local buckling at the intersection area was the main energy dissipating mechanism. Comparison with an N-joint shows that the completely overlap joint performed better under seismic loadings. After calibration by the experimental results, an extensive finite element analysis was carried out to determine the main factors that have significant influence on the hysteresis behavior of the joint.