A　speed　perturbation　model　is　proposed　in　this　paper　for　the　heterogeneous　platoon　to　measure　the　interaction　between　vehicles　and　investigate　the　propagation　laws　of　perturbations.　Then,　a　ratio　is　defined　to　quantify　the　relationship　between　the　communicating　information　impact　(CII)　and　the　car-following　behaviour　impact　(CFI).　A　modified　IDM　is　employed　to　evaluate　the　role　of　communicating　information　in　perturbation　propagation.　Results　show　that　communicating　information　can　suppress　the　amplification　of　perturbation.　Under　the　stable　environment,　the　interaction　between　vehicles　decreases　with　frequency.　There　is　a　critical　frequency　omega(c)　(value　of　0.55　in　this　case)　that　distinguishes　the　relationship　between　the　CII　and　CFI.　When　the　frequency　is　smaller　than　omega(c),　the　CFI　is　larger　than　CII;　otherwise,　the　CII　dominates　the　interactions　between　vehicles.　Under　the　unstable　environment,　the　interaction　between　vehicles　increases　first　and　decreases　then,　where　the　vehicles　are　mainly　affected　by　the　car-following　behaviours.