The steel plate-to-sleeve connection with overflowed grout is a novel rebar connection method for prefabricated components which indicates a promising use. It transforms the rebar connection into that between the steel plate and the sleeve, thus minimizing the rebar locating difficulty, simplifying the connection configuration, and improving construction efficiency. The shear performance of the steel plate-to-sleeve connection with overflowed grout is examined, wherein a shear test is conducted to examine the parameters of the sleeve constraint form and shear key spacing. The results demonstrate that: (1) The damage of the specimens is characterized by the crushing of the grout near the shear key. (2) The shear capacity of the specimens with enclosed sleeves increases by 165.5% compared with that of the specimens with unenclosed sleeves. (3) When the shear key spacing increases from 60 to 100 mm and 150 mm, the shear capacity of the specimens decreases by 11.1% and 35.3%, respectively. Moreover, the finite element models of the steel plate-to-sleeve connection with overflowed grout based on ABAQUS software are established considering the interface relationship. The results match well with the shear test results. On this basis, the effects of the height of the shear key (6, 8, and 10 mm), the spacing of the shear key (60, 75, and 100 mm), the strength of the grout (C60, C85, and C100), and the thickness of the grout (25, 30, and 35 mm) on the shear performance of the steel plate-to-sleeve connection with overflowed grout are primarily investigated. The parameter analysis results show that the shear capacity is positively correlated with the shear key height and grout strength, negatively correlated with the shear key spacing, and slightly affected by the grout thickness.