In this research, as pore-forming agents, silica poly-hollow microspheres were added into Si₃N₄ slurries, and Si₂N₂O phase was generated by the liquid phase sintering reaction between SiO₂ and Si₃N₄. Moreover, the space occupied by the silica poly-hollow microspheres would become the pores after the sintering process, and porous Si₂N₂O ceramics were fabricated. The morphology and mechanical properties of porous Si₂N₂O ceramics could be well regulated by adjusting the solid loading of Si₃N₄ slurry. The results show that with the increase of Si₃N₄ slurry solid loading, the content of Si₂N₂O phase increases and their porous structure has great changes. Besides, their open porosity decreases to 51.7% and their flexural strength increases to 26.74 MPa.