An electrochemical method of scanning electrochemical microscopy（SECM）was developed for the detection of extracellular reactive oxygen species（ROS）based on H2O2.The release of ROS was investigated by SECM technique after stimulation of lung cancer cells（A549）with tetradecanoylphorbol acetate（PMA）.The distance between the electrode and petri dish was determined as about 8 μm,and the cell morphology was shown clearly with hexamineammonium chloride（Ru（NH3）6Cl3）as the solution mediator in negative feedback mode.The release of ROS from A549 cells treated with PMA in real time were evaluated using SECM imaging when the potential of the probe was set at -0.65 V.Expanding the imaging range,SECM images of the release of ROS from different cells and the real time capture of ROS signals were obtained.Overall,the PMA induced ROS production was successfully determined.Moreover,at the corresponding ROS release site,the current variation with time was fluctuating.It was speculated that the release of ROS from cells was a dynamic pulsation process in this condition.