Sandwich insulation wall panels (SIWPs) are used extensively as thermal resistance components in buildings. Connectors in SIWPs are subjected to axial and shear forces to resist the load of the outer layer and transfer it to the inner layer and structure. In some areas, the insulation thickness needs to increase to achieve a satisfactory heat preservation effect, which leads to an increase in connector length. Most existing connectors do not satisfy the mechanical requirements for a thick insulation layer, e.g., 300 mm. In this work, a series of pull-out and shear tests were conducted for a novel long glass fiber-reinforced polymer I-shaped connector. The ply design and anchorage design of the connectors are key factors that affect the connector’s mechanical properties. Through comparative tests, the influence of these two factors on the axial and shear stiffness, capacity, and failure mode were explored. The addition of ±45° and 0°/90° multiaxial fiber cloth had little effect on axial performance, but the vertical shear stiffness and horizontal shear capacity improved. The pull-out and vertical shear capacity can be improved by optimizing the anchorage design and adding a row of anchorage rebar in the flange.