This　paper　analyzes　the　relationship　between　fuel　rail　pressure　and　fuel　injection　amount　and　presents　a　diagnosis　algorithm　for　coherence　of　injection　in　cylinders　based　on　the　fuel　rail　pressure.　A　simplified　model　of　common-rail　fuel　system　in　multi-cylinder　diesel　engine　was　built　and　basic　analysis　was　completed　based　on　this　model.　The　analysis　induced　that　the　rail　pressure　drop　dp/dt　is　mainly　relevant　with　QInj.　The　experimental　investigation　of　common-rail　fuel　system　shows　the　pressure　drop　happens　during　the　fuel　injection　period,　which　is　induced　by　fuel　injection.　Both　model　analysis　and　experimental　investigation　show　that　the　rail　pressure　may　be　used　as　the　basis　of　diagnosis　for　coherence　of　fuel　injection.　©　(2012)　Trans　Tech　Publications,　Switzerland.