For　a　class　of　mismatched　uncertain　multiple　input　multiple　output　linear　systems　with　state　time　delay,　a　new　self-tuning　sliding　mode　control　method　is　proposed　based　on　the　linear　matrix　inequality　theory.　In　this　method　a　sufficient　condition　for　the　existence　of　linear　sliding　surface　is　given　according　to　the　linear　matrix　inequality　theory,　while　in　the　sliding　phase　such　that　the　system　is　restricted　to　the　switch　surface　and　completely　invariant　to　mismatched　uncertainties　and　state　time　delay.　For　controller　output　chattering　case,　the　Sigmoid　function　instead　of　sign　function　is　introduced　and　a　self-tuning　sliding　mode　controller　is　further　designed.　Under　the　self-tuning　law,　the　Sigmoid　function＇s　boundary　layer　and　switching　gain　can　be　adjusted　automatically,　which　can　reduce　the　high　frequency　chattering　of　outputs.　The　Lyapunov　theory　is　applied　to　prove　the　stability　of　this　new　control　method.　Finally,　the　simulation　results　of　an　example　are　investigated　to　show　the　feasibility　and　effectiveness　of　the　proposed　approach.