The invention discloses a supported phosphorus molybdenum heteropoly acid low temperature SCR catalyst and a preparation method thereof, and belongs to the field of air pollution technology preventionand control. The supported phosphorus molybdenum heteropoly acid low temperature SCR catalyst is obtained by supporting vanadium-modified phosphomolybdic acid serving as an active component on TiO2,and the mass of the active component in the catalyst is 5-20% of the total mass of the catalyst. By adopting the supported phosphorus molybdenum heteropoly acid low temperature SCR catalyst, the activity and denitration efficiency of the catalyst can be effectively improved under the low temperature condition, the sulfur and water resistance performance is high, the method is simple in preparation, and the denitration cost is low.