A composite structural board, comprising: a face plate comprising a main body portion that is substantially flat and a peripheral portion surround the main body portion formed by the main body portion extending downwards, the face plate having an upper surface and a lower surface; a base plate provided with a plurality of protrusions which are substantially uniformly distributed and integrally formed, the lower surface of the face plate is attached to and supported on top faces of the protrusions ; and a stiffener for connecting the peripheral portion of the face plate and the base plate , wherein a cross-section of the stiffener is of a closed frame shape, at least a part of the closed frame shaped cross-section is connected to a bottom surface of the base plate , and at least a part of a vertical surface of the stiffener located outside is connected to at least a part of a lower surface of the peripheral portion of the face plate wherein the peripheral portion of the face plate is configured to extends downwards along a direction substantially perpendicular to the main body portion to form an extension portion, the stiffener is configured with a hollow structure with a rectangular cross-section, a top surface of the stiffener is substantially parallel to the main body portion of the face plate and abuts against a lower surface of the base plate to be fixed closely with the lower surface of the base plate , and a lower end of the vertical surface is configured to protrude outwards along a horizontal direction to form an integral flange onto which a free end of the extension portion of the face plate is supported, such that an end of the flange is substantially flush with an outer surface of the extension portion, and characterised in that a flange of the stiffener is provided at its lower side with a wing extending downwards therefrom. a face plate comprising a main body portion that is substantially flat and a peripheral portion surround the main body portion formed by the main body portion extending downwards, the face plate having an upper surface and a lower surface; a base plate provided with a plurality of protrusions which are substantially uniformly distributed and integrally formed, the lower surface of the face plate is attached to and supported on top faces of the protrusions ; and a stiffener for connecting the peripheral portion of the face plate and the base plate , wherein a cross-section of the stiffener is of a closed frame shape, at least a part of the closed frame shaped cross-section is connected to a bottom surface of the base plate , and at least a part of a vertical surface of the stiffener located outside is connected to at least a part of a lower surface of the peripheral portion of the face plate wherein the peripheral portion of the face plate is configured to extends downwards along a direction substantially perpendicular to the main body portion to form an extension portion, the stiffener is configured with a hollow structure with a rectangular cross-section, a top surface of the stiffener is substantially parallel to the main body portion of the face plate and abuts against a lower surface of the base plate to be fixed closely with the lower surface of the base plate , and a lower end of the vertical surface is configured to protrude outwards along a horizontal direction to form an integral flange onto which a free end of the extension portion of the face plate is supported, such that an end of the flange is substantially flush with an outer surface of the extension portion, and characterised in that a flange of the stiffener is provided at its lower side with a wing extending downwards therefrom. <EOS>