A composite light guide plate comprises a light guide plate and a prism structure adhering to the light guide plate. The light guide plate comprises a light emitting surface. A plurality of first microstructures is formed on the light emitting surface. The prism structure is adhered on the light emitting surface of the light guide plate. The prism structure comprises a first surface in contact with the light emitting surface. A plurality of second microstructures is formed on the first surface. Each second microstructure is corresponding to and in tight contact with one of the first microstructure. An apparatus and a method for manufacturing the composite light guide plate is also provided.