A fertilizer grinding mechanism, a water and fertilizer mixing device, and an aqueous fertilizer solution preparation production line. A fertilizer receiving body, where an edge is provided with a arranged first channel; a connecting body, fixed to a bottom of the fertilizer receiving body and provided with a second channel with the first channel, a bottom of the second channel is communicated with a buffer bin, a pushing block is arranged in the buffer bin, and the pushing block is connected with a drive mechanism for driving the block to move in direction of the body; and an inner grinding block, where the block is fixed to a bottom of the connecting body, an outer side of the inner grinding block is with a vertically movable grinding roller, the pushing block can push fertilizer under vertical movement of the roller. The grinding mechanism has a heat dissipation effect.