Previous studies found that people automatically represent others’ tasks just as representing their own. But the mechanism of shared representations remains unknown, more precisely, we do not know whether the representations for oneself and others are separated or separated. In the present study, we developed a new paradigm by combining the working memory Ponzo illusion and the Social Simon task to investigate the mechanism of shared representations. Results showed that when four Ponzo figure lines were distributed into two parts for two participants to remember, the working memory Ponzo illusion effect occurred (the upper line is recalled longer than the lower one), which was consistent with the results obtained in the condition when one person was required to remember four Ponzo lines (Experiment 1). These results suggested that in social situation, people automatically represented other’s task information and integrated it with their own, just as if all tasks had been their own. Moreover, the integration is stable and not influenced by different social interaction types such as cooperation and competition (Experiment 2).