Pei Songzhi annotated the history of the Three Kingdoms, not only by visiting the ruins, researching the events of the Three Kingdoms, listening to the memories of the elderly, but also by consulting books and researching the recorded place names, people and events. He classified his annotations into four categories: filling gaps, preparing differences, punishing mistakes and arguing. Among them, the first two types of annotations supplement what Chen Shou left out, accounting for the vast majority of Pei's annotations, so the Qing Dynasty's "Sikuquanshu Catalogue Summary" subdivided these two types into four items.
The latter two types of annotations refute obvious mistakes and comment on historical events or Chen Shoushu, which are generally titled "Chen Song Case" or "Chen Song Thought". Although the overall number is small, it is highly valued by scholars because it can better highlight Pei Songzhi's historical consciousness.