The invention discloses a method for preparing alloy powder by roasting cold-rolled sludge. The method comprises the following steps that cold-rolled sludge powder is mixed with calcium oxide powder and carbon powder according to the ratio; then the mixed material is roasted for 2-3 hours at the temperature of 900-1000 DEG C under the gas protection; and the roasted material is ground into powderafter being cooled to the room temperature, and then is added with water for dissolution, then impurity removal and cleaning are carried out to obtain the cleaned material, namely the alloy powder material. According to the method, by heating the cold-rolled sludge, the calcium oxide and the carbon powder, under the reduction action of the carbon, the metal ions are converted, namely, the metal ions are converted into elementary substances from the ions, and the alloy powder is obtained, wherein the calcium oxide can play a role in combination with Cl ions, then a soluble substance can be formed, and volatilization of Cl is avoided; and the raw material adopted by the method is the cold-rolled sludge, the alloy powder is directly obtained through high-temperature roasting reduction, the yield is high, the process is short, an additive is cheap and easy to obtain, and other accessory reactants are decomposed or inhibited under the action of the roasting temperature and the additive.