The invention discloses a quantitative type liquid fertilizer filling mechanism. The quantitative type liquid fertilizer filling mechanism comprises a material barrel, a piston, a guide rod, a transmission rod, a sealing seat, a valve seat, a valve element, an end cover, a mounting seat, a minisize air cylinder, guiding grooves, limiting strips, a liquid inlet joint and a liquid outlet joint. When liquid enters, the transmission rod drives the piston to move downwards, so that the guide rod extends out along the sealing seat; negative pressure is generated in a cavity formed by the upper end of the piston and the material barrel; and a liquid fertilizer enters the cavity in the upper end of the piston through the liquid inlet joint, a liquid inlet and a main channel, and thus liquid inlet is completed. When the liquid is discharged, the minisize air cylinder pushes the valve element to move forwards along the valve seat, and the limiting strips fixedly connected with the valve element slide in the guiding grooves; and after the minisize air cylinder is in place, the liquid outlet joint, a liquid outlet, the main channel and a material barrel cavity communicate with one another, and the transmission rod pushes the piston to move upwards, so that the liquid fertilizer is extruded through the liquid outlet joint. The quantitative type liquid fertilizer filling mechanism is simple and compact in structure; filling of the liquid fertilizer can be conducted quantitatively; precision is high, and the integration level is high; intermediate control elements such as solenoid valves are not needed; and production cost is lowered.