A sizing composition for glass fiber direct roving for producing multiaxial fabrics is provided. The sizing composition includes, based on the total solids mass of the composition, 0.1 to 5.0% by solid mass of a first silane coupling agent, 2.5 to 11.0% by solid mass of a second silane coupling agent, 3.0 to 20.0% by solid mass of a first film former, 45.0 to 75.0% by solid mass of a second film former, 0 to 5.0% by solid mass of a plasticizer, 0.2 to 4.0% by solid mass of a first lubricant, 5.0 to 20.0% by solid mass of a second lubricant, and 0.01 to 3.0% by solid mass of a pH regulator. The first film former is a multifunctional epoxy emulsion, and the second film former is a low-molecular-weight liquid epoxy emulsion. The sizing composition has a suitable dissolution rate in the resin and good compatibility with the resin. It enables the wind turbine blades made from glass fiber multiaxial fabrics containing the sizing composition to have such advantages as stable mechanical strength, excellent fatigue resistance, and longer service life.