To achieve the coordination of mechanical properties and tribological performance of ceramic-based materials, a novel Si3N4/Ni composite with a tree-trunk ring structure was developed in this study. Furthermore, the tribological properties of the Si3N4/Ni composite were investigated in a high-humidity environment. The results showed that when the Si3N4/Ni composite disc slid against the Si3N4 pin, a continuous water layer formed on the wear surface of the composite disc due to their good hydrophilicity and the action of gravity. The water layer inhibits the abrasive wear and promotes the formation of tribochemical film. Under the combined effect of the water layer and tribochemical film, the sliding pair exhibited excellent tribological properties (a low coefficient of friction (COF) of 0.05 and wear rate on the order of 10−6 mm3/Nm). However, when the Si3N4/Ni composite pin slid against the Si3N4 disc, due to poorer hydrophilicity and the negative effect of gravity, the sliding pair presented a worse tribological performance.