The　parameters　n　and　b　in　Rosin-Rammler　(R-R)　size　characteristic　equation　were　studied　by　analytic　geometry　and　partial　derivative　method.　The　analyses　include　not　only　the　relationship　between　the　parameters　and　the　particle　size,　but　also　the　effect　of　parameters　n　and　b　on　the　particle　size　distribution.　And　the　conclusion　is　verified　by　some　examples.　The　results　show　that　b　mainly　affects　oversized　cumulative　productivity　R　when　d＜＞exp(1/b).　The　larger　n　is,　and　the　more　uniform　particle　size　distribution　becomes.　When　0＜d＜1　mm,　the　smaller　n　is,　the　more　uniform　particle　size　distribution　becomes.　Moreover,　the　above　theoretical　results　can　fully　explain　the　particle　size　distribution　characteristics　under　different　crushing　and　grinding　conditions.　©　2015,　Central　South　University　of　Technology.　All　right　reserved.