Abstract: The thermal decomposition effect of amino poly phosphate powder is considered to be an important reason for its explosion suppression feature. To reveal the effect of amino poly phosphate(NH4 H2 PO4 ) powder on the inhibi- tion of methane explosion,the author investigated the effect of thermal decomposition products(ammonia and phosphor- us pentoxide)of NH4 H2 PO4 powder on the methane explosive process. A test with the self-improved 20 L spherical gas explosion experimental system of XKWB-1 was conducted to test the influence that these two products would have on the process of methane explosive individually,and a comparative analysis of two products’ influence level on the in- hibiting process was carried out. The result shows that the thermal decomposition products( ammonia and phosphorus pentoxide)of NH4 H2 PO4 powder have a certain weakened effect on methane explosion,and the weakened effect of NH3 (one thermal decomposition product) is greater than the weakened effect of P2 O5 ( another thermal decomposition product),this appearance is even more significant for the high volume fraction of methane.