In the paper, the flower-like Cu2O had been obtained in the distilled water under very low reaction temperature. This hydrothermal method provided a homogenous environment for the nucleation and growth of the Cu2O. The reaction temperature, time, solvent, and additives would affect the purity and morphology of samples. When the reaction temperature was greater than 90 degrees C, elementary copper appeared in the as-obtained sample. With the reaction temperature and time increase, the morphologies also had been changed. The changing process of these morphologies had also been discussed. When ethanol amine replaced some or all of the aqueous solution, the resulting product is pure copper. Meantime, the effect of copper sources and additives on purity and morphology of products were investigated. Finally, the optical properties and PEC properties of the flower-like Cu2O were studied. This paper provided a very simple and low cost method to synthesis of flower-like Cu2O, which would be of great potential for the synthesis of other metal chalcogenides.