NH4V3O8 flower, nanobelt, lath and sheet were synthesized using a facile microwave hydrothermal method. The formation mechanism of NH4V3O8 with various structures was proposed. As an cathode in Li-ion battery, the NH4V3O8 nanobelt with one-dimensional structure as well as nanosized morphology, presents excellent cycling stability and enhanced rate capability when comparing with other NH4V3O8 structures. Further study finds that the NH4V3O8 nanobelt could provide high Li ion diffusion, excellent structural stability and good reversibility during the charge/discharge process, indicating a strong connection between the morphology and the electrochemical performance of NH4V3O8 cathode.