Composite slabs with trapezoidal steel sheets have been extensively used in composite flooring systems. Sinusoidal steel sheets can be fabricated with relatively thicker steel plates and employed in smooth-curved structures such as buried culverts, thus exhibiting a relatively wider application range than trapezoidal steel sheets. Study has rarely been conducted on composite slabs composed of concrete cover and relatively thick sinusoidal corrugated steel plates. This study focus on the bending behavior and longitudinal shear mechanism of composite slabs with sinusoidal corrugated steel plates. Four-point bending tests were conducted considering different slab thicknesses, shear connector types, and numbers. Partial interaction theory was adopted as the basis for the development of the corrugated-steel-plate–concrete composite slab theoretical model. A computer program named CSPC-SSA (Corrugated-Steel-Plate–Concrete Simply-supported Slab Analysis) was written based on partial interaction theory and finite difference method. The Modified Newton-Bisection algorithm was developed to balance the calculation time and accuracy. It can be concluded that the newly proposed shear connector exhibits similar strength and deformation behavior compared to the conventional shear connector, and that the flexural strength of the corrugated-steel-plate–concrete composite slab was positively correlated with the shear connector number and concrete cover thickness. Improperly increasing the concrete cover thickness may cause longitudinal shear failure.