The invention discloses a sulfur hexafluoride and nitrogen mixed gas density variation monitoring system which comprises a main control unit, a gas sensation detection unit and a gas concentration detection unit, wherein the gas sensation detection unit and the gas concentration detection unit are respectively connected with the main control unit through data signal lines; the detection end of the gas concentration detection unit and the gas sensation detection unit are both arranged at high-pressure opening/closing equipment. The invention further discloses a sulfur hexafluoride and nitrogen mixed gas density variation monitoring method. As the main control unit of the sulfur hexafluoride and nitrogen mixed gas density variation monitoring system adopts the gas sensation detection unit and the gas concentration detection unit to obtain parameters such as pressure, temperature and concentration of a mixed gas in real time, the density value of the mixed gas can be finally obtained by using a multi-element composite algorithm, and in addition, detection values such as temperature, pressure, concentration and density of the mixed gas can be displayed on a screen in real time, record data can be automatically stored by the system, and convenience can be brought to later data investigation and study through a history checking function.