Objective To investigate variations of event related potential N400 in childhood absence epilepsy (CAE). Methods The Guangzhou Runjie WJ-1 ERP instrument was employed to perform N400 tests for 45 cases of CAE and 42 normal children by the use of model of normal words (matching) and ambiguous words (mismatching) ended Chinese sentences. Results  ①Latency. Compared with the control group, the CAE group showed prolonged N400 latency in three encephalic regions (Cz、Fz, and Pz), especially for both matching (P<0.01) and mismatching (P<0.01) indexes in the Cz region, as well as in Fz and Pz regions. ②Amplitude. Compared with the control group, the CAE group also showed much lower N400 amplitude in five encephalic regions, especially for both matching (P<0.01) and mismatching (P<0.01) indexes in the Cz region. Conclusion Sentence ending words are a favorable stimulus to elicit N400, which can be used for clinical neurology, especially for auxiliary diagnosis of CAE.