Tunnel-type β-MnO2 cathode materials are synthesized by adopting simple hydrothermal method with its application to aqueous ammoniumion batteries, shows excellent electrochemical performance within a voltage window range of 0~1.6 V by using 1 mol/L (NH4)2SO4 aqueous electrolyte. The experimental results show that β-MnO2 cathode materials exhibit a discharge specific capacity of 109.8 mAh/g at a current density of 0.1 A/g. After 140 cycles, its discharge specific capacity still reaches as high as 101.9 mAh/g, with a capacity retention rate of 92.8% and a Coulombic efficiency close to 100%, demonstrating an excellent cycling stability. Meanwhile, β-MnO2 nanorod cathode material is characterized with an excellent rate performance, with a discharge specific capacity of 78.7 mAh/g at a high current density of 1.0 A/g. In addition, an inquiry has been made into the energy storage mechanism based on ex situ FTIR and XPS testing, with the results showing that the ammoniumions exhibiting a good reversibility.