A novel electrochemical atomic force microscope (EC-AFM) operating in liquid or electrolyte is developed. The special EC-AFM probe contains a tip attached a cantilever, a laser source, a position sensitive detector and a Plexiglas glass which meanwhile can be used as a tip holder. The laser optical path in liquid also owns a special design. The cantilever and the sample are immersed in fluid completely when the system works. In addition, an open electrolytic cell has been designed which enables to change the sample’s liquid environment and control the electrochemical process conveniently. Besides, when the system works, the probe tip scans over the sample surface to escape the confines of the specimen size and weight. Using the EC-AFM system, the experiment of copper plating on an iron plate in copper sulfate solution is carried out and real-time investigated. During the plating process, the AFM images of the sample surface are acquired directly in the copper sulfate with nano-scale resolution. The results show that the EC-AFM system can observe the solid-liquid interface of the electrochemical reactions and processes directly.