The invention discloses a solar energy-based rainwater collecting and fallen leaf crushing fermenting device. The solar energy-based rainwater collecting and fallen leaf crushing fermenting device comprises a fermentation chamber, a steel wire gauze, an extruding system, a water spray roller system, a cylinder cover system, a rainwater collecting system, a ventilating system, and a solar energy supply system; an extruding plate, the steel wire gauze, and the water spray roller system are used for realizing secondary extruding and smashing of materials, and primary spraying of materials; material smashing is beneficial for full fermentation, and is capable of improving fertilizer quality; in fermentation, a gas inlet extruding plate and a gas outlet extruding plate are pushed forward, gas is introduced into the fermentation chamber via a gap, the steel wire gauze and the water spray roller system are used for increasing gas flow turbulence, sufficiency oxygen is provided by gas, and heat energy is discharged together with gas; the rainwater collecting device is used for collecting and simple purifying and storing of rainwater, and a device water source is provided; the solar energy supply system is used for providing device electricity, and realizing green processing; and the main body of the solar energy-based rainwater collecting and fallen leaf crushing fermenting device is arranged underground, so that space is saved.