Abstract: Ultra-High Performance Concrete (UHPC) has a great potential for the application in composite construction and steel structure strengthening. The interface between UHPC and steel plate is important to the composite behaviour of the entire structure. In this paper, five kinds of interface between non-steam-cured UHPC and steel plate were investigated through a series of pure-tensile and push-out tests. The interface treatments included smooth plate; embossed plate; epoxy based adhesive with sprinkled-in aggregates, pre-bent steel rebar welding; and headed stud connecting. The results shows that UHPC has low and unreliable adhesion to the steel plate; the embossed steel-plate interface and the epoxy based adhesive interface have higher adhesion strength but brittle failure under tensile or shear loads without constraint; the pre-bent steel rebar welding and headed stud connecting treatments demonstrate evident regularity and ductility after initial interface adhesive failure, but little increase on shear capacity is observed by imposing constraint. Furthermore, the behavior of stud connection interface was specially discussed in this paper. It was found that classic theory and current codes of practice significantly underestimate the capacity of cone failure of UHPC, and an assumption of variable angle failure surface was suggested. In addition, an exponential function model for the load-slip relationship of headed studs in UHPC was calibrated and verified by the test results.