Randomly selecting 20 university students (10 female, 10 male) as subjects, who were right-handed and had passed CET-4 and Manipulating different anomaly types (semantically, syntactically or doubly anomalous sentences) and anomaly words at sentence-internal and sentence-final position, the study probed into Chinese ESL learners’ mental mechanisms of English active sentence processing by using ERPs. Specifically, the experimental materials included 360 active sentences whose length ranges from 6 to 8 words and were classified into six types (each type includes 60 sentences): control sentences, sentence-internal syntactic anomalies, sentence-internal semantic anomalies, sentence-final syntactic anomalies, sentence-final semantic anomalies and sentence-internal and sentence-final double anomalies involving both semantic and syntactic difficulties. The task of subjects was to judge whether the sentences were correct. In addition, the indices of the observation were reaction times, the rate of correct responses and ERP indices in the process of the experiments.