The invention relates to a preparation method for cuprous 
oxide micron / nano 
crystal with controllable morphology, relating to the preparation method for the cuprous 
oxide micron / nano 
crystal. The invention mainly solves the technical problems of high cost and environmental 
pollution in the preparation process of the micron / nano cuprous 
oxide. The method comprises the following steps of: 1, dissolving 
copper salt into 
ultrapure water, pouring 
lactic acid, continuously stirring, regulating a pH value, cooling to the temperature of 25 DEG C, keeping constant volume, measuring the pH value, and obtaining solution A; 2, moving the solution A to a 
hydrothermal reaction kettle, sealing the reaction kettle, putting the 
hydrothermal reaction kettle into a 
drying oven, keeping the temperature, naturally cooling to a 
room temperature, centrifugally washing by using the 
ultrapure water, centrifugally washing by using 
anhydrous ethanol, transferring the reaction kettle onto 
watch glass, and 
drying the reaction kettle in the 
drying oven; and thus obtaining the cuprous oxide micron / nano 
crystal. The preparation method for the cuprous oxide micron / nano crystal with the controllable morphology has the 
advantage of simpleness and practicability, simple equipment operation, low 
raw material price, easy synthesis, less 
pollution to environment and high synthetic concentration, the problem of the cost of the 
morphology control and industrialized large-scale synthesis in the prior art is solved, and the industrial production is facilitated.