Steel-UHPC composite bridge deck system can overcome the shortcoming of orthotropic bridge deck with the fatigue crack and the damage of bridge deck pavement. In order to investigate the transverse bending performance of the composite deck system, the static positive and negative moment loading tests were carried out on 20 steel-UHPC composite slabs, and the effect of different parameters on their interface and bearing performance was analyzed. The results show that under the action of negative moment, the transverse flexural tensile property of the composite slab can be improved by properly increasing the reinforcement ratio. The crack distribution of cast-in-place slab is dense at bending stage, the denser of crack increases with the increasing of the reinforcement ratio. However, the cracks of precast slab are sparse. Under the positive moment loading, the elastic limit and cracking load are larger than those under the negative moment. Because the large interface bonding strength between the steel and UHPC, the interface is still not separated, when the composite plate yields. The cracking strength of steel-UHPC composite slab changes 8.9 to 22.2 MPa, which is larger than 6.41 MPa. It can be seen that the interface can meet the requirement of engineering.