[en] Highlights: • Largely enhanced photocatalytic properties in the visible light region. • The shape-controlled Cu₂O crystals are obtained by adjusting the reaction condition. • A plausible growth mechanism of Cu₂O nanostructures was proposed. An interesting evolution to prepare shape-controlled Cu₂O nanocrystals was realized by a convenient one pot synthesis. The Cu₂O nanocrystals with different shapes can be obtained simply by adjusting the composition of reaction system. And, a plausible mechanism was also proposed to explain the nanostructures formation. The surface of Cu₂O spheres with thorn exhibited high photocatalytic activity on the degradation of methyl orange (MO) solution under visible light irradiation. The photodegradation efficiency of MO solution reach up to 99.67% at the first 10 min. It is still as high as 98% even at the end of the fourth cycle.