Abstract: The use of pultruded glass fiber-reinforced polymer (GFRP) strips as sandwich spar caps of wind turbine blades can overcome the manufacturing defects such as wrinkles and bubbles caused by conventional fiber cloth laying process. It can also improve the modulus and strength of the material as well as reduce the manufacturing cost, and hence becomes one of the promising manufacturing techniques for wind blades in the future. To investi-gate the influence of the face sheet thickness and the shear-span ratio on the strength and failure modes of the sandwich spar cap, a series of sandwich specimens with biaxial GFRP face sheets and pultruded GFRP strips core were tested by four-point bending. The test results show that with the increase of the face sheet, the failure mode of the specimen changes from the rupture of pultruded GFRP strip for the specimen without face sheet, to the damage or rupture of GFRP face sheet for the specimen with single layer face sheet, and to the delamination for the specimen with multilayer face sheets. The failure mode could be controlled by proper design of the ratio between the core and face sheets. Also, the initial stiffness of the sandwich spar cap increases with the increase of the face sheet thickness and with the decrease of the shear-span ratio. Increasing the face sheet thickness could improve both strength and ductility of the test specimens, and could delay the cracking of the glue seam as well as reduce the sudden loss of maximum load.