The thermal decomposition behaviors of ammonium perchlorate (AP) and AP/Al/HTPB composite solid propellant in the presence of magnesium based hydrogen storage materials(Mg ₂NiH ₄,Mg ₂Cu-H and MgH ₂)were studied by DSC. The results show that 5% magnesium based hydrogen storage materials has obvious catalytic effect on the thermal decomposition of AP,and 1.3% magnesium based hydrogen storage materials obviously decreases the thermal decomposition temperature and increases heat release of AP/Al/HTPB composite propellant. The burning rates of AP/Al/HTPB composite solid propellant (8 MPa) are increased by 3.5%, 14.4% and 13.9% respectively with addition of 1.3% Mg ₂NiH ₄, Mg ₂Cu-H and MgH ₂. There is a clear relationship between hydrogen content of magnesium based hydrogen storage materials and its effect, and MgH ₂ shows obvious effect among magnesium based hydrogen storage materials due to its large hydrogen content. By catalyzing the thermal decomposition of AP, magnesium based hydrogen storage materials shows good catalytic effect on thermal decomposition of AP/Al/HTPB composite solid propellant.