A　simple　method　is　proposed　to　optimize　the　thickness　parameter　of　the　boundary　layer　of　the　saturation　function　in　the　Complementary　Sliding　Mode　Control　(CSMC).　A　pair　of　complementary　sliding　surfaces　are　constructed.　And　the　Taylor　series　is　used　to　estimate　the　steady-state　error　of　CSMC　system　to　optimize　the　parameter　value　for　the　boundary　layer　of　the　saturation　function　without　artificial　settings.　This　proposed　CSMC　strategy　is　applied　to　the　speed　regulation　in　permanent　magnet　synchronous　motor　with　lump　uncertainties.　The　experimental　results　show　that　the　proposed　CSMC　strategy　can　obtain　an　optimal　value　for　the　boundary　layer　parameter,　effectively　suppressing　the　chattering,　and　keep　an　excellent　system　performance.　©　2019,　The　Editorial　Department　of　Journal　of　Harbin　Institute　of　Technology.　All　right　reserved.