Based　on　the　mechanical　rock　breaking　platform　of　Beijing　University　of　Technology,　the　linear　cutting　test　is　performed　with　disc　cutters　on　the　composite　rock　mass　composed　of　mudstone　and　green　sandstone,　to　explore　the　relationship　between　the　rock　debris　features　and　the　penetration　after　rock　breaking　with　disc　cutters.　During　the　test,　six　sets　of　different　penetrations　(1.0　mm,　3.0　mm,　5.0　mm,　7.0　mm,　9.0　mm　and　11.0　mm)　are　set　to　collect　the　rock　debris　generated　from　rock　breaking　with　the　disc　cutters　at　different　penetrations.　The　Rosin-Rammler　function　is　used　to　analyze　the　rock　debris　data,　and　the　characteristic　particle　size　theory　is　used　to　analyze　the　optimal　penetration　during　rock　breaking　with　the　disc　cutters.　Furthermore,　a　method　based　on　the　characteristic　particle　size　theory　is　proposed　to　determine　the　optimal　penetration.　Through　comparative　analysis,　it　was　found　that　the　optimal　penetration　obtained　using　the　characteristic　particle　size　theory　is　consistent　with　the　optimal　penetration　obtained　through　specific　energy,　which　verifies　the　effectiveness　of　the　proposed　method;　and　this　method　is　more　direct　and　convenient.　©　2023　Editorial　By　Modern　Tunnelling　Technology.　All　rights　reserved.