两者其实区别不大,你如果一定要鸡蛋里挑骨头,则有这样的解释：

　　1、从语气上来说,-ing形式比较personal和friendly,和lookforwardto...相比较少为正式,如果你要表示礼貌而有亲和力则用lookingforwardto...,lookforwardto在非常正式严谨的business场合比较适用.

　　2、国外英语论坛上nativespeaker给的解释二：

　　“Thedifferenceishowthespeakerperceivestheirownwords:

　　anactionseenasawhole/accomplished(Ilookforward...)orcontinuing(Iamlooking...).

　　一个动作的结束（lookforwardto...）和一个动作的持续（lookingforwardto...）

　　Unlessveryself-awareorpossiblyanEnglishteacher,anordinarynativespeakerwillbeunabletoexplaintheirchoicebetweenthetwoandsothedifferencebetweenamentalimpression(Ilookforward)andamentalactivity(I'mlookingforward).Insuchcases,attemptingtoexplainthesesubtletiestoyourstudentsmayprovecounterproductive,unlessofcoursethey'readvancedenoughtohandleit.Itismypolicy,thatuntilthenthey'reperfectlyfineknowingthereisnorealdifferencethere.”