The precursor of aluminum-doped zinc oxide nanocrystals modified by nitrogen atoms (N-AZO) can be quantity-produced by ultrasonic hydrothermal equipment. Then the N-AZO photocatalysts with good visible-light response were synthesized via solid-phase method with urea as a nitrogen source. The ultraviolet visible (UV-vis) patterns of N-AZO nanocrystals obviously showed a red shift toward the visible-light region compared to pure aluminum-doped zinc oxide (AZO) nanocrystals and an absorbance in the wavelength range of 450-600 nm which was attributed to the change of lattice structure after nitrogen doping. The photocatalytic activity of N-AZO photocatalysts were investigated by the degradation of RhB solution in sunlight irradiation. The ratio of nitrogen atoms to Zn atoms had significant impact on the photocatalytic efficiency of N-AZO nanocrystals. The experimental results showed that the optimal doping mole ratio of urea molecules to zinc atoms was 6:5, and the RhB dyes were degradated completely within 2 h, exhibiting that improved photocatalytic activity increased by 400% compared with that of pure AZO nanocrystals. What is more, a feasible water purification reactor with continuous photodegradation was manufactured which was also suitable to degrade other kinds of organic pollutants by changing the effective photocatalyst. The result showed that when the flow velocity of RhB solution (2 x 10(-5) g/L) was 60 mL/min, the degradation rates of the four reactors were about 38%, 48%, 62.5%, and 100%, respectively.