Previous studies have shown that the effect of emotional distractor on information storage in Working Memory (WM). The activity of fronto-parietal cortex related to WM is reduced when task irrelevant emotional stimuli presented. Furthermore, the interference effect of acute stress on WM is modulated by the WM load, and this effect was showed on the P3 component. However, how the emotional distractor affects the central executive function, i.e., information refreshing, of WM is not clear. To this end, an emotional N-back task was conducted combine with EEG technique. In this task, the WM load and valence of emotional distractor was manipulated. Participants were performed a digital 2-back or 0-back. In the 0-back task, participants were asked to detect whether the current digit is “1” or not. In the 2-back task, participants were asked to detect whether the current digit is presented two positions back or not. The neutral or negative emotional picture was presented under the digit in each trial. The behavioral results showed that there is a significant main effect of WM load, the participant response faster in the 0-back task than in the 2-back task, and they made less error in the 0-back task than in the 2-back task. For the P3 component, we found significant main effect of WM load, the amplitude of P3 for the 0-back task were larger than for the 2-back task. Furthermore, in the 0-back task, negative distractor elicited smaller P3 than the neutral distractor. However, in the 2-back, the difference between negative and neutral distractor is not significant. These results can easily explain by the recently proposed dual competition model which positing that emotional and cognitive processes, when operating simultaneously, compete with each other for limited neural resources. Specifically, processing of emotional stimuli may interfere with ongoing cognitive processes when cognitive resources are not entirely devoted to goal-directed processing under a lower task demanding condition. In contrast, the interference effect is attenuated due to the suppression of emotional processing under a high task demanding condition.