Discharge　even　breakdown　accident　may　happen　to　the　switchgear　cabinet　because　of　the　electric　field　concentration　of　contact　box　during　long-term　operation　and　the　use　of　double　shield　structure　is　an　effective　way　to　improve　the　electric　field　distribution　at　the　contact　box　of　the　switchgear　cabinet.　Therefore，type　KYN28A　-　12　switchgear　cabinet　is　taken　as　the　research　object　and　a　three-dimensional　electric　field　optimization　method　based　on　SVM-PSO　hybrid　algorithm　for　the　double　shield　structure　in　the　contact　box　of　the　KYN28A-12　switchgear　cabinet　is　proposed.　Firstly，a　three-dimensional　simulation　model　of　the　switchgear　cabinet　is　set　up　in　the　Comsol　Multiphysics，and　the　influence　of　the　length　of　earth　shield，the　radius　and　length　of　high　voltage　shield　on　the　surface　field　strength　of　contact　box，earth　shield　and　high　voltage　shield　are　analyzed.　Then，the　evaluation　function　of　the　surface　field　strength　of　contact　box，earth　shield　and　high　voltage　shield　is　constructed，and　a　prediction　model　of　the　evaluation　function　with　different　length　of　earth　shield，radius　and　length　of　high　voltage　shield　are　set　up　by　SVM　algorithm.　Finally，the　PSO　algorithm　is　used　to　optimize　the　evaluation　function　to　obtain　the　optimization　result　of　structure　parameters　of　the　double　shield　in　the　contact　box.　In　order　to　verify　the　correctness　of　the　optimization　result，a　three-dimensional　electric　field　simulation　is　developed　and　the　relative　error　is　4.8%.　The　partial　discharge　of　the　optimized　contact　box　under　1.2　Ur　is　1.38　pC，which　verifies　the　effectiveness　of　the　optimized　results.　The　research　results　provide　a　theoretical　basis　for　the　design　and　optimization　of　double　shield　in　the　contact　box　of　the　switchgear　cabinet.　©　2023　Xi＇an　High　Voltage　Apparatus　Research　Institute.　All　rights　reserved.