Abstract: The manufacture of phosphoric acid from phosphate rock by wet process has been studied. The pilot plant consists of two systems, digestion system(I) and filtration system (II) . In(I),five reaction tanks are arranged in series. The ground phosphate rock is fed into the first tank. Sulfuric acid mixed with weak phosphoric acid returned from (II) is fed into the second one. The digested slurry from the last tank is pumped to a vacuum flash cooler, where most of heat is removed. The cooled slurry flows back into the first tank with a circulating ratio of 13~15:1. In (II), a continuous horizontal tilting-pan type filter is used, which comprises 15 seperate filter pans having a total filtering area of 1.5 square meters. The pans can be filled automatically. The filter cake, which is subjected to two counter-current washes, can be unloaded by automatically overturning the pans. The recovery of soluble P2O5 from filtration is >99% . The maximum capacity of the filter is 800 kg. dry cake/M2-hr.. The acid produced (from the first filtrate) is 30~32%P2O5.