Under joint action of vortex-induced vibration（VIV）of stay cable and random traffic loading on bridge deck，field observation on VIV of a stay cable and stress measurement at details of an anchor box are carried out to investigate its stress behavior and fatigue performance at all connection details of the steel anchor box in a long-span cable-stayed bridge. The rainflow counting method is employed to obtain the stress range at those details，while the nominal stress approach is used to evaluate fatigue performance of the anchor box. The research found that the multi-mode VIV occurs under weather condition of no rain and low wind speed with wind direction approximately normal to the bridge axis，and the VIV is characterized by participation of two or several sequent high-order modals or two groups of several sequent high-order modals，with the in-plane peak acceleration significantly larger than the out-of-plane one，and the measured maximum acceleration of 24 m/s2. Under one truck loading，details on the anchor box present stress behavior similar to main structural components，with only one stress cycle generated and a very long stress influence line at all details. For those measured stress time histories，the VIV of the stay cable does not impose on additional fluctuating stress cycles featured with high-order mode vibration，implying that loading by VIV on the steel anchor box can be ignored. It is recognized that the detail of the upper and lower plate to the outer web weld of anchor box mainly transfers shear stress，while its stress at the deck side is not only higher than that at the weld center and the lower end，but also higher than that at other details，with the maximum stress range of 46.6 MPa at the end of upper plate to the outer web at the deck side. It is concluded that except the detail at the deck side of the upper and lower plate to the outer web weld，other details own infinite fatigue.