The invention provides a pin penetrating mechanism for a horizontal-type pressing machine for biomass scrimbers. The pin penetrating mechanism comprises pin penetrating air cylinders mounted on the pressing machine, a row of pin ejecting rods of the pin penetrating air cylinders, a row of pin storing boxes corresponding to the pin ejecting rods, a pressing machine die cavity corresponding to the pin storing boxes, and locks inside the die cavity. The pin penetrating air cylinders and the pin ejecting rods connected with the same are transversely arrayed and vertically arranged. A pin feeding cage capable of moving in and out of the pressing machine is positioned below the pin ejecting rods and above the pressing machine die cavity. The pin storing boxes are sequentially disposed in box grooves of the pin feeding cage. A row of pin falling holes are formed in a front base plate of the box groove of the pin feeding cage along the length direction and are provided with pin falling controllers. The pin falling holes correspond to a row of pin penetrating holes in an upper die plate of the die cavity below the pin falling holes. Pin penetrating holes in the upper die plate of the die cavity correspond to die-locking pin holes of the locks inside the die cavity. The die cavity of the horizontal-type pressing machine lies horizontally, and the locks lie horizontally in the die cavity, so that die-locking pins can be penetrated the locks from the upward sides of the locks in the vertical direction.