The invention relates to a production method and apparatus of hollow granular water-soluble 
fertilizer. The production method comprises the following steps: adding 
phosphoric acid, 
urea, 
potassium salt and micro 
fertilizer into a mixer, and preparing mixed 
slurry; then adding the mixed 
slurry in a foaming device, reacting and foaming, obtaining viscous 
slurry, pumping the viscous slurry into a rotary differential spray head, scattering the slurry into liquid drops by virtue of the spray head, enabling the liquid drops to drop in a solidifying device, thermally polymerizing and solidifying intohollow particles, and subsequently cooling and screening to obtain a final product. The apparatus comprises a 
urea transport unit, a 
phosphoric acid transport unit and a 
potassium salt transport unit, as well as a mixer, a foaming device, a solidifying device, an 
exhaust gas treatment unit and an after-
treatment unit which are communicated with the units. By adopting the production method, additional 
foaming agent and instant-soluble additives are not needed, 
carbon dioxide gas generated during the reaction is fixed inside the granular water-soluble 
fertilizer to change the internal physicalstructure of the granular water-soluble fertilizer product so as to achieve an instant soluble effect, the hollow granular 
water soluble fertilizer meeting different technological requirements can beacquired, the product is unlikely in 
moisture absorption and 
caking, and the dissolving rate is increased.