The invention discloses a method for preparing CZTS (Copper Zinc Tin Sulfide) (Se) series nanometer powder by low-temperature mechanical alloying. Elementary substances Cu powder, Zn powder, Sn powder and S (Se) powder are added into a ball-milling tank according to a certain mole ratio, an alcohol and amine mixed liquor is used as a process control agent, ball milling is carried out according to a rated ratio of grinding media to material, a set rotational speed and ball milling time, and a ball-milled product is centrifugally washed and dried to obtain a target product. In the raw materials, elementary substances sulfur powder and selenium powder can be exchanged in any mole ratio; and the process control agent is the mixed liquor of alcohol and amine with the volume ratio of 1-20:1, the alcohol is one of ethanol, ethylene glycol, normal butanol, isobutanol, isoamylol, tertiary amyl alcohol and glycerol, and the amine is one of ethanediamine, iso-butylamine, diisopropylamine, hexamethylenediamine and triethylamine. The method disclosed by the invention has the advantages of easy obtainment of raw materials, pure products, low energy consumption, easy control in product shape and appearance, simple process and the like, and is suitable for industrial production.