This　study　investigates　the　non-linear　shear　behaviors　and　failure　mechanisms　of　rock-like　materials　with　three-dimensional　joint　regarding　various　sample　diameters　(d),　joint　roughness　coefficients　(JRC),　and　joint　wall　strength　ratios　(SR).　A　series　of　cylindrical　specimens　were　prepared　and　underwent　direct　shear　tests.　The　peak　shear　stress　(tau(max))　decreases　by　13.09%-25.98%　with　an　increasing　d　due　to　the　intensified　stress　concentration　resultant　from　a　diminished　contact　area.　A　higher　JRC　increases　tau(max)　by　13.16%-50.70%　due　to　enhanced　interlocking　effects.　An　increase　in　SR　improves　the　matrix　mechanical　properties,　resulting　in　a　gentle　growth　in　tau(max)　by　7.30%-18.27%.　The　normal　displacement　(delta(v))-shear　displacement　(u)　curves　and　failure　morphologies　of　the　joints　indicate　that,　as　d　decreases　or　JRC　and　SR　increase,　the　curves　gradually　move　upward　and　the　failure　modes　of　the　joints　transfer　from　plastic　shear　flow　to　brittle　shear　failure.　Furthermore,　the　finite　element　method　simulation　was　introduced　to　analyze　the　mesoscopic　wear　characteristics　of　the　joint　surfaces.　The　results　reveal　that　the　process　of　joint　failure　can　be　categorized　into　three　stages　including　wear,　shearing,　and　further　smoothing,　and　the　failure　degree　on　the　joints　exacerbates　with　a　smaller　d　or　larger　JRC　and　SR.　Additionally,　an　improved　non-linear　shear　failure　criterion　considering　the　influences　of　size　effect,　SR,　and　JRC　is　developed　based　on　the　Barton＇s　JRC-JCS　(joint　compressive　strength)　model,　with　the　average　error　reduced　significantly　from　8.12%　to　3.23%.