The invention relates to a composite catalyst for preparing hydrogen through supercritical water gasification of low-moisture-content dehydrated sludge and an application of the composite catalyst, and belongs to the field of composite catalysts for preparing hydrogen through supercritical water gasification of dehydrated sludge. The composite catalyst for preparing hydrogen through supercritical water gasification of the low-moisture-content dehydrated sludge comprises the following raw materials in parts by mass: 50-75 parts of active nickel and 25-50 parts of a carbon fixation agent, wherein the carbon fixation agent is one of NaOH, KOH, Ca(OH)2, CaO, CaSiO3 or Na2SiO3. The composite catalyst provided by the invention can be used for catalyzing the low-moisture-content dehydrated sludge at a relatively low reaction temperature (400 DEG C) to generate hydrogen, the catalytic efficiency is high, the cost is greatly saved, and by using the composite catalyst and under the condition with 5% of add amount, a hydrogen-rich gas of which the hydrogen content reaches 88% can be generated, the hydrogenation efficiency is improved and the catalytic effect is significant.