In order to clarify the influence of design parameters on the mechanical behavior of a cable-stayed bridge of a floating system，a finite element model of the bridge was established by using the finite element analysis software MIDAS/Civil based on a single-tower double-cable plane steel-concrete composite beam cable-stayed bridge with full floating spatial frame.The sensitivity of parameters such as temperature effect，secondary dead load，and support system in the completed bridge state was analyzed and compared with the semi-floating system of the bridge.The results show that temperature and secondary dead load have a significant impact on the deflection and stress of the main beam.Overall，the sensitivity of the deformation and stress of the main beam of the full floating system to various parameters is lower than that of the semi-floating system.After the structural system is converted from full floating to semi-floating，the first-order natural frequency increases from 0.38 Hz to 1.09 Hz，and the overall stiffness of the structure is significantly improved.Under seismic excitation，the overall displacement of the full floating system is greater than that of the semi-floating system，but the bending moment of the tower root structure decreases.