Since it is requested that the smashed straw should not be scattered onto the stubble in the first season harvest, a smashing and scattering device matched with the first season harvester of ratoon rice was designed in this paper to smash and scatter the straw into the rolling area. The main structural parameters affecting the straw scattering performance were determined by theoretical analysis of the deflecting performance of the straw deflector. EDEM software was used to simulate and analyze the straw scattering situation under the action of the deflector. Taking the qualified rate of straw scattering as the performance index, the optimal parameter combination of the straw deflector was determined by L27 (313) orthogonal test, and the operating performance of the device was verified by bench test and field comparison test. The test results show that: The optimal parameter combination was 45° between the straw deflector and the vertical direction, 200 mm height difference between straw deflector and outlet, 0° inclination angle of inner deflector and 35° inclination angle of outer deflector. The qualified rate of straw scattering was 72.2% in the corresponding simulation test, 93.6% in the bench test and 95.2% in the field test, which could meet the demand of first season harvest of ratoon rice.