The invention discloses a preparation method of a low-temperature NH3-selective catalytic reduction (SCR) catalyst for exhaust gas of gas boilers. The method comprises the following steps: separatelypreparing inorganic salts of Fe, Mn and X (X is one of Sm, Ce, Zr, Co, Cr, Ni and Cu) into a solution with a molar concentration of 0.5-1 mol/L, and mixing the obtained solutions to obtain a solutionD; preparing alkali into a solution with a molar concentration of 0.5-0.7 mol/L, and dropwise dripping the obtained solution into a vessel containing the mixed solution while vigorously stirring; by adjusting the dripping rate of the alkali solution, controlling the pH value of the titration end point to be 9-10, continuously stirring for 30-40 minutes, standing for 3-6 hours, and then filtering;washing a filter cake for 3-5 times with distilled water until the washing liquid is neutral, and drying to obtain a precursor of the catalyst; putting the precursor of the catalyst into a muffle furnace, and calcining for 4-5 hours at 500-550 DEG C in the air atmosphere so as to obtain the low-temperature NH3-SCR catalyst for the exhaust gas of the gas boilers. The catalyst prepared by the methodis high in low-temperature catalytic activity, strong in water resistance and low in price, thus having important practical and economic significance.