In　order　to　suppress　uncertainties　caused　by　parameteric　variations　and　disturbances,　a　sliding　mode　control　(SMC)　optimized　by　a　second　order　terminal　sliding　mode　control　(STSMC)　was　derived　to　control　current　loops　in　a　permanent　magnet　synchronous　motor　(PMSM).　The　equivalent　control　quantity　for　the　current　loop　is　easily　obtained　by　SMC.　The　switching　control　for　uncertainties　was　deduced　by　STSMC　integrated　with　an　adaptive　exponential　function　law.　Moreover,　the　stability　of　STSMC　system　was　analyzed　for　current　loops,　and　the　gain　of　the　switching　function　in　STSMC　can　be　set　small,　even　to　be　set　theoretic　zero.　STSMC　is　effective　to　suppress　the　“chattering”　and　retains　the　system　robustness.　The　comparative　results　of　simulations　and　experiments　indicate　that　the　current　loop　control　system　by　STSMC　improves　the　steady　state　accuracy　of　the　current　with　the　result　in　a　better　performance　of　speed　regulation　for　PMSM,　and　is　easy　to　implement.　©　2018,　Harbin　University　of　Science　and　Technology　Publication.　All　right　reserved.