The utility model relates to a straw smashing device of a field straw smashing chopper. The straw smashing device comprises a casing (1), L-shaped smashing cutters (2), linear smashing cutters (3), separation sleeves (4), fixed cutters (5) and pins (6). The straw smashing device is characterized in that two L-shaped smashing cutters, one linear smashing cutter, a separation sleeve and a pin from a straw smashing movable cutter group; the L-shaped smashing cutters are arranged on two sides, the linear smashing cutters are disposed in the middle, the separation sleeves separate the L-shaped smashing cutters from the linear smashing cutters, and the L-shaped smashing cutters, the linear smashing cutters and the separation sleeves are hinged on the pins; the linear smashing cutters are 3cm to 5cm longer than the L-shaped smashing cutters and disposed between two corresponding fixed cutters; and the fixed cutters are fixed on the inner surface of the casing. Included angles beta between cutting edges and bottom sides of the fixed cutters (5) are smaller than or equal to 45 degrees, and the cutting edges are plain edges or serrated edges. By means of the straw smashing device, crop straw fallen on the ground can be effectively picked up, support cutting and smashing is performed on crop straw, and the straw smashing quality is improved.