The present invention relates to a secondary battery electrolyte, which includes a composite electrolyte salt; the composite electrolyte salt comprises lithium hexafluorophosphate, lithium difluorosulfonate, and lithium sulfide salts; the lithium sulfide salts include substituted sulfates (R1—SO3—Li) and/or sulfonate structure lithium salts (R2—O—SO3—Li). The present invention employs a combination of LiPF6, lithium sulfide salts, and LiFSI, where LiFSI exhibits better hydrolysis stability, superior thermal stability, and higher lithium migration capability, significantly enhancing the battery's kinetics and high-temperature performance. Lithium sulfates and sulfonate structure lithium salts also possess high lithium migration capabilities. Moreover, their anion groups rich in S and O form films that improve the composition of the SEI film and reduce membrane impedance, thereby enhancing the battery's kinetic and high-temperature performance.