High　slope　efficiency　3　mu　m　laser　output　exceeding　Stokes　limit　is　demonstrated　in　Er:YAG　crystals　with　lower　doping　concentration　at　room　temperature.　Based　on　cyclic　cascaded　cavity,　several　parameters　affecting　slope　efficiency　are　optimized.　Under　the　optimized　configuration,　slope　efficiencies　up　to　36.5%　and　37.2%,　exceeding　the　Stokes　efficiency　of　33%,　are　achieved　in　10at.%　and　25at.%　Er:YAG　crystals,　respectively.　The　realization　of　high　slope　efficiency　paves　the　way　for　improving　the　average　power　of　3　mu　m　lasers.