The timecourse of the interaction between syntactic and semantic information during sentence processing is investigated using event related potentials (ERPs). With the "ba" sentences, the present study examines brain responses to syntactic-only violation conditions, semantic-only violation conditions and doubly violation conditions. The specific procedure of the experiment is shown in Figure 1. The LAN effect is compared between syntactic-only violation sentences and doubly violation sentences. As shown in Figure 2, the doubly violation sentences give rise to longer latency (p<0.01) and larger amplitude (p<0.01) and more widely cortex distribution (p<0.05) than the syntactic-only violation sentences(see Figure 3&4). In the earlier stage of the syntactic processing, the completeness of the semantic information affects the LAN effect, there is an interaction between syntax and semantics in this stage. The N400 effect is compared between semantic-only violation sentences and doubly violation sentences. As shown in Figure 5, they don't have significant difference between the amplitude (p>0.05) and distribution (p>0.05), while the lack of the syntactic information in the doubly violation sentences prolongs the time of the sentence processing (p<0.01). In this stage, the processing of semantics is influenced by syntactic information, there is also an interaction between syntax and semantics in this stage. The P600 effect is compared between syntactic-only violation sentences and doubly violation sentences. As shown in Figure 2, they have the slightly different amplitude and highly different distribution, the doubly violation sentences give rise to larger positive component(p>0.05) and more widely cortex distribution (p<0.05). The P600 effect is reduced in the doubly violation sentences as compared to the P600 elicited in a syntactic-only violation sentences, the incompleteness of the semantic information affects highly the processing of the whole sentence, there is an interaction between syntax and semantics in this stage as well. These results suggest that semantic and syntactic information are integrated during the earlier stages of sentence processing indexed by the different LAN effect, and these interactions continue in the other stages of processing indexed by different N400 effect and the reduction of the P600. This study provides evidence supporting parallel processing model.