Visual working memory (VWM) maintains and manipulates a limited set of visual objects being actively used in visual processing. To explore whether and how the fine detailed information is stored in VWM, four experiments have been conducted while recording the contralateral delay activity (CDA), an event-related potential difference wave that reflects the information maintenance in VWM. The type of the remembered information was manipulated by adopting simple objects and complex objects as materials. We found the amplitude of CDA was modulated by object complexity: as the set size of memory array rose from 2 to 4, the amplitude of CDA stopped increasing for maintaining complex objects with detailed information, while continued increasing for storing highly discriminable simple objects. These results suggest that VWM can store the fine detailed information; however it can not store all the fine detailed information from 4 complex objects. It implies that the capacity of VWM is not only characterized by a fixed number of objects, there is at least one stage influenced by the detailed information contained in the objects. These results are further discussed within a two-stage storing model of VWM: different types of perceptual information (highly discriminable features and fine detailed features) are maintained in VWM via two distinctive mechanisms.