The present disclosed invention relates to a quick switching mechanism for the side
discharge unit and the
chopper unit of a
lawn mower: a side
discharge unit and a
chopper unit are mounted at the grass outlet on a
cutting platform; wherein, the side
discharge unit comprises a grass discharging gear shaft, a grass discharging hood mounted on the grass discharging gear shaft; the grass
chopper unit comprises a grass chopping gear shaft, a grass chopping closing plate mounted on the grass chopping gear shaft; the small gear on the grass discharging gear shaft is engaged to the big gear on the grass chopping gear shaft; a guy wire is mounted on the
cutting platform, and is connected to a rotary arm mounted on one end of the grass chopping gear shaft. In the invention, the current grass discharging hood is kept, and therefore the safety of grass discharging is not compromised; during the mowing process, when the
mower runs into a place (e.g., a kerb,
shrub, etc.) where the grass discharging process is difficult, the
mower can be switched from grass discharging mode to grass chopping mode immediately; after the mower passes the place, it can be switched back to grass discharging mode quickly; if the mower runs into a narrow place (e.g., the space between two trees), the mower can be switching from wide discharging mode to narrow discharging mode immediately; the mower can be switched back quickly after it passes through the place.