一、句子分析：
主要成分：we need to have it
后置定语：on which to base our policy
二、该定语是个不定式短语,其中
1.which 指代上文的代词 it,因此 on which to base our policy = to base our policy on it；
2.由上可知 to 是动词不定式符号
3.base sth.on ...意思是“把...建立在...的基础上
三、可以把它改写为从句：
We need to have it on which we can base our policy.
或者：We need to have it which we can base our policy on.
四、翻译：我们需要拥有（或得到）把政策建立在它上面的这个东西(it 上文提到过,可以用上文提及的名词取代本译文中的“这个东西”).