Photovoltaic　(PV)　power　generation　has　attracted　many　attentions　for　a　decade.　Both　two-level　and　three-level　inverters　are　commonly　used　topologies　to　feed　the　power　into　the　three-phase　electric　grid　system.　Further,　the　three-level　neutral　point　clamped　inverter　is　always　applied　to　the　transformerless　photovoltaic　grid-connected　system　because　of　its　low　leakage　current　and　the　low　voltage　stress　comparing　with　the　two-level　inverters.　In　the　transformerless　grid-connected　PV　inverter　system,　both　reliability　and　the　efficiency　are　important　factors.　Because　of　no　isolation,　the　common-mode　voltage　of　the　inverter　must　be　low　to　prevent　adverse　effects　from　the　leakage　current.　Further,　the　switching　loss　must　be　low　to　have　high　efficiency.　In　this　paper,　a　low　switching　loss　PWM　strategy　with　low　common-mode　voltage　applied　to　three-level　grid-tied　inverter　is　shown.　Comparing　with　the　conventional　carrier-based　phase　disposition　PWM,　both　common-mode　voltage　and　the　switching　loss　are　improved.