有区别，意思相同，用法不同，on behalf of是介词短语，repersent是动词。
on behalf of
英 [ɔn biˈhɑ:f ɔv] 美 [ɑn bɪˈhæf ʌv]
为了…的利益;代表…
【例句】
He spoke on behalf of all the members of the faculty and staff.
他代表全体教职员工讲了话。
Secret Service officer Robin Thompson spoke on behalf of his colleagues.
特工处官员罗宾·汤普森代表他的同僚发表了讲话。
On behalf of my Government I have the honour to make to you the following communications.
我荣幸地代表我国政府向您转达如下内容。
The settlement ends more than four years of litigation on behalf of the residents.
这一和解协议结束了代表居民提起的超过四年之久的诉讼。
On behalf of everyone here I want to thank you for your help.
我代表在场的各位感谢你帮助了我们。
represent
英 [ˌreprɪˈzent] 美 [ˌrɛprɪˈzɛnt]
vt.
表现，象征;代表，代理;扮演;作为示范
vi.
代表;提出异议
第三人称单数： represents 现在分词： representing 过去式： represented 过去分词： represented
【例句】
The offer has yet to be accepted by the lawyers representing the victims.
受害者的代理律师还没有接受这个提议。
The general secretary may represent the president at official ceremonies.
总书记可以在一些官方仪式上代表主席。
My only aim is to represent Britain at the Olympics.
我唯一的目标是代表英国参加奥运会。
Women are already well represented in the area of TV drama
女性在电视剧领域占据了一席之地。