The steel-UHPC lightweight composite deck is a novel bridge deck pattern that consists of an orthotropic steel deck（OSD） and a thin ultra-high performance concrete（UHPC） layer. In order to reveal the effect of UHPC layer on the performance of the OSD, field measurement was performed for Fengxi Bridge to evaluate the stress ranges in the typical detail categories of the OSD with/without UHPC layer, respectively. Before the field measurement was conducted, the global finite element model of Fengxi Bridge was developed to determine the instrumented sections. Then, a triaxial loading vehicle, according to the loading scheme，was arranged to run on the bridge deck with/without UHPC layer at a low speed, respectively. The field measurement data of the typical detail categories were collected and sorted. Finally, a local finite element model of Fengxi Bridge was built to compare with the field measured results. The field measurements show that the stress response of the typical detail categories are significantly reduced after installment of UHPC layer. For the detail categories related to the steel deck（i.e., rib-to-deck weld, deck splices, and deck of rib-to-deck at diaphragm joint），the stress range decreased by about 75% ~ 90%；for the detail categories related to the trapezoidal rib（i.e., rib splices, weld end of rib-to-diaphragm joint, and rib of rib-to-deck at diaphragm joint），the stress range decreased by about 65% to 80%; for the detail categories related to the diaphragms（i.e.，cut-out on diaphragm, diaphragm base metal at cut-out transition, and diaphragm of rib-to-deck at diaphragm joint），the stress range decreased by about 20% to 50%. Meanwhile, with the decrease of the distance from detail categories to top surface, the contribution of UHPC layer to the stress reduction of the detail categories was significantly increased. The results of the local finite element model agreed well with the measured results, and the similar rules were obtained. The field measured results of this paper provide the reference data for the application of steel-UHPC lightweight composite bridge deck.