The　existence　of　discrepancy　between　the　discretized　numerical　boundary　of　meshless　particle　method　and　the　assumed　real　one　is　proved　by　the　mechanism　analysis　based　on　the　notion　of　particle　number　density.　By　simulating　the　movement　of　scattered　fluid　particles　in　the　vicinity　of　boundaries　under　typical　cases　and　analyzing　their　trajectories,　such　difference　is　verified.　What＇s　more,　the　way　of　the　boundaries　exert　influences　on　flows　and　its　related　phenomena　are　conspicuously　demonstrated.　The　results　show　that　the　numerical　boundaries　do　not　exactly　represents　the　real　physical　ones　and　their　influences　zone　to　fluid　are　not　smooth,　which　lead　to　deflect　and　error　for　the　near　wall　flows,　especially　for　the　scattered　fluid　particles　with　low　velocity.　©　2014,　Science　Press.　All　right　reserved.