To study the properties of grouped stud connectors in prefabricated steel-UHPC composite beam under different stress states, three series of push-out tests and two series of tension-shear tests were carried out. The effects of stud spacing, aspect ratio and the ratio of tension to shear on failure modes, bearing capacity and ductility of grouped stud connectors in UHPC composite beams were considered. The expression of load-slip relationship of grouped stud connectors in UHPC is proposed. The results show that the failure mode of push-out test and tension-shear test was governed by stud fracture. Under the shear load, decreasing the stud spacing reduced the bearing capacity and ductility of grouped stud connectors. The aspect ratio of stud represented little influence on the ultimate bearing capacity and the relative slip of grouped stud connectors, which illustrated that the short stud could still play the shear performance in UHPC. It is recommended that the stud spacing of grouped stud connectors should not less than 4 times stud diameter and the grouped stud connectors in UHPC can be designed based on elastic theory. When the ratio of tension to shear is 0.17, the influence of tensile force on the mechanical properties of the stud connectors is negligible. When the ratio of tension to shear is 0.27, the tensile force obviously decreased the bearing capacity and ductility of grouped stud connectors in UHPC. The proposed load-relative slip model can accurately describe the behavior of stud connectors in UHPC decks.