Abstract: The definition of safety integrity level of ESD and the applied safety standard is mainly represented, the existing problems in the ESD current security situation of the 7 branches of the Chongqing Natural Gas Purification Plant General by illustrating are also analyzed. Based on SH/T 3018-2003 Design Code for Safety Instrumented System in Petrochemical Industry, SY/T 10045-2003 Application of Safety Instrumented Systems for the Process Industries, HG/T 20511-2000 Design Code for Signal Alarm and Safety Interlock System, the safety integrity level of ESD and some relevant suggestions for its improvement are proposed to increase the safety integrity level of ESD, hence, it can ensure the smooth running of natural gas purification device.