Large　surface　areas　while　maintaining　a　low　mass　transport　resistance　is　a　critical　criterion　for　the　optimal　design　of　electrode　structures　for　aqueous　redox　flow　batteries.　However,　for　conventional　micro-scale　electrode　structures,　increasing　surface　areas　will　lead　to　an　increase　in　the　mass　transfer　resistance.　In　this　work,　a　composite　electrode　with　a　gradient　porosity　distribution　is　fabricated　through　combining　two　different　carbon　felt　layers　of　different　porosities.　The　smaller-porosity　layer,　offering　a　larger　surface　area,　is　placed　adjacent　to　the　membrane,　while　the　larger-porosity　layer,　providing　a　smaller　mass　transfer　resistance　is　placed　on　the　flow　field　side.　The　thickness　ratio　of　the　two　layers　is　adjusted　in　terms　of　the　battery　performance　while　applied　in　the　vanadium　redox　flow　battery.　It　is　demonstrated　that　the　battery　with　the　structure-optimized　composite　electrode　achieves　a　high　energy　efficiency　of　82.7　%　at　200　mA.cm(-2)　at　an　electrolyte　flow　rate　of　30　mL.min(-1),　and　delivers　a　discharge　capacity　of　240　mAh　at　400　mA.cm(-2),　which　is　2.18　times　that　of　the　conventional　graphite　felt　electrode.　This　work　offers　an　idea　for　the　structural　design　of　high-performance　aqueous　redox　flow　batteries.