Abstract: To identify the compressive stability of the steel-ultra-high performance concrete (UHPC) composite deck structures in the light-weight composite girder systems of cable-stayed bridges, based on the test parameters including steel flange thickness, UHPC layer thickness, and stiffener shapes, five steel and steel-UHPC composite deck specimens with a geometric scale ratio of 1∶2 were designed and fabricated, and their compressive stability was investigated experimentally. The results show that: Steel specimens exhibit branch point instability mode, and the composite specimens possess high post-buckling bearing capacity with extreme point instability mode due to the strengthening effect of UHPC layer and the internal stress/force redistribution characteristics between steel and UHPC layer on the section where the steel is subjected to local buckling. Setting a 30 mm UHPC layer on the steel specimens can increase their elastic axial stiffness and compressive stability bearing capacity by 102.1% and 119.7%, respectively. Compared with the steel specimens with the same transformed cross-sectional area, the compressive stability bearing capacity of the steel-UHPC composite specimens can still be increased by 22.2%. The T-rib, which has the same cross-sectional area and moment of inertia around the strong axis as the U-rib, has better local stability; however, due to its lower torsional performance, the steel-UHPC composite specimens reinforced with T-ribs suffer overall flexural-torsional buckling failure, but the bearing capacity is similar to those of the specimens reinforced with U-ribs. A calculation formula for the bearing capacity of steel-UHPC composite decks under compressive stability was proposed based the different mechanical behaviors of steel and steel-concrete composite compressive members, and the applicability of formula was verified by the experimental results.