Abstract: To evaluate the application feasibility of HFO-1336mzz(E) mixed gas in high pressure gas insulation equipment, the configuration scheme of HFO-1336mzz(E) mixed with three buffer gases is calculated, and the power frequency insulation strength of HFO-1336mzz(E) is obtained through tests. In this paper, the critical molar proportions of HFO-1336mzz(E) in the gas mixture is obtained by calculating the saturated vapor pressure under the constraint conditions of –15 ℃, –20 ℃, and –25 ℃, and the power-frequency breakdown test is carried out for the HFO-1336mzz(E) gas mixture with these proportions. The results show that HFO-1336mzz(E) has the best synergistic effect when mixed with air. With −15 ℃ as the minimum operating temperature constraint, the maximum breakdown voltage of 0.5 MPa 8.0% HFO-1336mzz(E)/92.0% Air mixture is only 65% of SF₆ at the same pressure, which is equivalent to the insulation level of 0.26 MPa SF₆, and solid deposits appear after discharge of the mixture gas. The liquefaction temperature, insulation strength, and discharge deposits of the gas mixture are taken into consideration, and it is concluded that the application of HFO-1336mzz(E) gas mixture in high pressure gas insulation equipment has limitations.