During comprehension, language users not only immediately integrate information from local sentence context, but also information from global discourse context for full understanding. In the present study, we examined whether the time course of these integration processes is constrained by language users' working memory capacity. Sentence and discourse stimuli were constructed. For the sentence stimuli, each sentence contained a critical word that was either congruent or incongruent with its preceding sentence context. For the discourse stimuli, each discourse contained four sentences with a target word embedded at the final sentence and the target word was either congruent or incongruent with the information provided at the first sentence of the discourse. Participants of high and low working memory span were instructed to read for comprehension. Our results showed that while the high span readers showed the N400 and P600 effects to semantically incongruent words, the low span readers only showed the P600 effect. This pattern was found regardless of whether the incongruent words were placed at sentence or discourse context. These results suggest that the low span readers are relatively delayed than the high span ones at both sentence- and discourse-level semantic integration and indicate that working memory functions have greater influence than context scope on the time course of semantic integration.