To study the whole-process structural performance of new spread slab beam bridges, this paper investigated the damage development and failure mechanisms from construction to in-service stages with beam clear spacing, beam number and prestressing steel arrangement as key parameters. The nonlinear numerical analyses were preformed on the bridge system with using ABAQUS software. Research outcome indicates that the beam failure and mixed beam-slab failure are two main failure patterns for this new bridge system. When the beam clear spacing is small, the deformation of all beams is consistent, and the ultimate strength is relatively higher, which is prone to the failure of beams. On the contrary, when the beam clear spacing is large, the transverse load transfer capacity is relatively weaker and the deformation-lag effect exists among different slab beams, resulting in the mixed beam-slab failure. For spread slab beam bridge cases with similar bridge width and span length, a relatively larger beam spacing value is unfavorable for the transverse load sharing, and the ultimate strength of the entire bridge system may be significantly reduced by 40%~50%. The bearing capacity of bridge cases with less beam numbers can be improved by increasing the prestressing steel amount, and the ultimate strength of a single slab beam may be increased by 10%~30%. However, the camber issue at the precasting stage should be handled with caution in the design. Compared with the integral casting concrete beam bridge, this composite beam bridge system is different in the displacement and stress responses obtained from the whole-process analysis, but their difference in the ultimate strength is small. In general, the new spread slab beam bridge system shows good strength and deformation capability, and the characteristics of light weight, low profile and easy construction, owning a good application prospect in China.