Many shear connectors may need to be arranged together in group to achieve the required shear strength in the design stage of the composite connection. In most practical situations the space to install the shear connectors may be limited. The shear strength of the individual Y-type perfobond rib shear connector may not be obtained if the Y-type perfobond rib shear connector layers are placed too much close to other adjacent layers. It has been investigated in the previous study that the total shear resistance of the flattype perfobond rib shear connector group may either increase or decrease depending on the spacing between the adjacent layers. This study is designed to verify the effect of the spacing between the adjacent layers of Y-type perfobond rib shear connectors and propose the proper design rule to estimate the shear strength in the multi-layer shear connectors. The double layer specimens with various spacings have been push tested. The minimum adjacent spacing for the specimens has been selected considering the limited distance due to the inclined Y-ribs to each other. The Y-ribs in the standard Y-type perfobond rib shear connector are inclined with 30-degree, and may bother the Y-ribs from the adjacent shear connector. Two different spacings of 120 mm and 300 mm are selected as the minimum and maximum distances. The maximum 300 mm spacing is selected considering the height of the shear connector. The parametric study for the spacings between 120 and 300 mm have been performed using the numerical FEM models. The numerical FEM model has been verified and improved based on the experimental test results. The effect of transverse rebar diameters is also examined. The shear resistance formula is proposed for the double layer shear connectors.