Uniform distribution in molecular level of ceramics could be achieved by polymer-derived method. Comparing to other methods, fewer crystal seeds existed in microstructure of polymer-derived ceramics, which made it more difficult to sinter. Up to now, few reports focused on the direct sintering of the polymer-derived ceramics. For silicon nitride sintering, the introduction of metal oxide additives caused defects in the lattice of silicon nitride because of oxygen atoms, which could affect the properties of thematerial. This work focused on the sintering behavior of polymer-derived ceramics and the issue of performance degradation caused by introducing oxygen elements in sintering additives. The metal elements were connected to the precursor molecule and formed the metal nitride sintering additives during pyrolysis process. The method could help to achieve the in-situ non-oxygen addition and uniformly mixing of sintering additives, and the followed low-temperature sintering could achieve the high-purity silicon nitride ceramics.