In order to investigate the mechanical behavior of RBP-UHPC （retard-bonded prestressed ultra-high performance concrete） cantilever beam， two full-scale RBP-UHPC variable section cantilever beams were tested based on the background of the cantilever stairs in Shanghai Opera House. The test results show that during the loading process， the key variable sections cracked in turn， and the cracks were most dense near the key sections. The farther away from the key variable sections， the shorter and sparser the cracks were. The failure position of the cantilever beam was 2.6 m away from the root of the beam. The closer the section was to the failure section， the sooner the strain of UHPC and rebar reached the elastic compressive strain of UHPC and the yield strain of the rebar. The safety margin of the failure section of the two beams was 1.97 and 1.81 respectively， which had good structural performance and can meet the strength requirements of practical engineering. A calculation model for the ultimate bending moment of RBP-UHPC π-shaped variable section cantilever beam with structural plate was proposed. Compared with the existing codes， the calculated results of the model in this paper were in the best agreement with the experimental results and were safer.