The invention discloses a quaternary phosphonium salt compound, a preparation method thereof and application thereof in electrochemiluminescence biological detection. The quaternary phosphonium salt compound is 1,12-bis(trioctyl phosphonium bromide)dodecane. After mixing of 1,12-dibromododecane with tri-n-octylphosphine, the reflux reaction is made by using trichloromethane as a solvent; the solvent is removed by rotary evaporation; and then recrystallization is performed by using ethyl acetate to obtain a quaternary phosphonium salt compound. A quaternary phosphonium salt/ZnTCPP system constructed by the ZnTCPP is loaded by using the 1,12-bis(trioctyl phosphonium bromide)dodecane as a carrier, thereby realizing electrochemiluminescence light-emitting signal detection of H2O2. The quaternary phosphonium salt compound has advantages of high ionic conductivity, wide electrochemical window, and high structural and functional designability as well as high thermal stability and electrochemical stability.