Abstract: Water soluble ammonium polyphosphate mainly containing ammonium pyrophosphate was used as the experimen tal raw material.Seven groups of pH gradients（8.2，6.0，4.0，3.5，3.0，2.5 and 2.0） were set up to systematically research the influence of pH on the hydrolysis of ammonium pyrophosphate.Combining the first order reaction kinetic equation and Arrhenius equation to calculate the hydrolysis kinetics of ammonium pyrophosphate.The results showed that the mass fraction of ammonium pyrophosphate successively decreased from initial 92.6% to 85.4%，51.2%，50.6%，50.2%，24.3%，12.9% and 6.0% after hydrolyzing 310 d（second batch of 260 d）.The hydrolysis rate of ammonium pyrophosphate under natural temperature conditions increases by varying degrees with the decrease of pH and it obeys the first order reaction.The hydrolysis rate constant of ammonium pyrophosphate increased from 2.92×10-4~3.43×10-4 to 3.41×10-3~1.47×10-2 when pH decreased from 8.2 to 2.0.The difference of both of them were 10~40 times，the corresponding half-life was 50~2 000 d. The hydrolysis rates of autumn winter and spring summer were very different.The hydrolysis rate constants of the two periods differ by 1.17~4.32 times，and the hydrolysis activation energy of ammonium pyrophosphate was in the range of 7.5~68.5 kJ/mol.

Key words: ammonium pyrophosphate；ammonium polyphosphate；hydrolysis；pH