Abstract: The present disclosure provides a lightweight spar cap with a concave structure for a wind turbine blade and a manufacturing method thereof, a wind turbine blade and a manufacturing method thereof. The lightweight spar cap is groove-shaped as a whole, and includes supporting portions located on two wings of the lightweight spar cap and an intermediate connecting portion connecting the two supporting portions. The manufacturing method of the lightweight spar cap includes laying a reinforcing body of the intermediate connecting portion and a supporting material of the supporting portion, and performing resin infusion. By comprehensively considering multiple factors, the present disclosure reduces the weight of the wind turbine blade, improves the material utilization of the wind turbine blade, and realizes a lightweight wind turbine blade.