In order to solve the engineering problem of continuous box girder bridges with severe cracking due to excessive self-weight， a combined PC and steel-UHPC composite beam continuous hybrid girder bridge is proposed. To investigate the mechanical properties of the UHPC layer in the new type of bridge as well as its effect on the force transfer mechanism of the joint section of steel-UHPC composite girder， a Midas integral FE model was established to obtain the internal force of the structure under the design load effect， taking Binzhou Yellow River Bridge in Shandong Province as the engineering background. Meanwhile， two FE sub-models of the joint section of the steel-UHPC composite girder with and without UHPC layer were established by using ANSYS， respectively. The differences between the two models in the force performance and load transfer mechanism of the steel-concrete joint section were compared， and the mechanical properties of the UHPC layer were analyzed. The FE results show that： 1） Except for some stress concentration areas， the stresses in all parts of the new structure are lower than the strength design value， meeting the design requirements； 2） Under the most unfavorable bending moment， the maximum tensile stress of the top plate of the new structure’s steel box girder is significantly reduced， which can significantly improve the fatigue life of the steel structure； 3） The stress at the interface of the top plate of the new structural concrete beam is decreased by about 5%~29%， which can improve the cracking resistance； 4） The maximum tensile and compressive stresses of the UHPC layer are lower than their design strength， meeting the design requirements， and the UHPC layer can share 4%~10.9% of the bending moment of the joint section.