Capillary　barrier　effects　(CBEs)　have　been　applied　in　capillary　barrier　systems　as　effective　means　of　protecting　underground　regions　from　wetting.　However,　the　microscale　behavior　of　CBEs　and　related　influencing　factors　are　not　well　understood.　This　study　utilized　microfluidics　to　investigate　effects　of　flow　rate　and　pore　size　variability　on　CBEs　at　the　microscale.　Imbibition　processes　of　water　displacing　air　were　imposed　on　three　water-wet　microfluidic　chips　with　different　degrees　of　pore　size　variability　and　injection　rates.　The　obtained　results　demonstrated　that　the　increasing　injection　rate　changed　water　invasion　pattern　from　finger　growth　to　compact　displacement.　The　CBEs　could　increase　Swf　(water　saturation　of　fine　sections　at　the　onset　of　breakthrough)　by　up　to　44%.　The　increase　in　Swf　became　smaller　at　a　higher　injection　rate　but　was　insensitive　to　the　pore　size　variability　within　the　investigation　range.　This　study　also　elaborated　the　specific　effect　of　inertia　on　pore　body　invasions　under　different　pore　characteristics.　Among　the　materials　with　close　average　pore　size,　those　with　more　uniform　pore　sizes　are　recommended　for　the　construction　of　capillary　barrier　systems.　For　capillary　barrier　systems　with　robust　CBEs,　increasing　the　thicknesses　of　coarse　layers　has　insignificant　effect　on　reducing　deep　percolation.