The invention provides a mixed gas density relay, comprising a sealed housing and a reference gas chamber located inside the sealed housing, a transmission connecting rod, a driving mechanism, a microswitch, a movement, a dial and a pointer; The microswitch is arranged at the fixed end of the reference air chamber, and the driving mechanism is arranged at the middle position of the transmission connecting rod. One end of the transmission connecting rod is connected with the machine movement, and the other end is fixedly connected with the movable end of the reference air chamber; The movementis connected with the pointer, which drives the pointer to indicate the density of the mixed gas intuitively on the dial. The mixed gas density relay only needs to fill the reference gas which is thesame quality as the mixed gas to be measured in the reference gas chamber, It has better adaptability, faster and better temperature compensation effect, consistent control accuracy in all the workingtemperature range of the mixed gas density relay, and can reliably trigger the micro-switch to send out alarm signal.