这两个词组基本都表示“占有”的意思，它们的区别在于:前者表示主语“占有…”，即主动占有;后者表示主语“被…占有”，即被动占有，它们一般与动词 be 搭配。
1. in possession of=possessing; having possession 存有，属于，拥有，掌握
The library is in possession of several sets of encyclopedias.
这家图书馆存有好几套百科全书。
As no pumas had reported missing from any zoo in the country, this one must have been in possession of a private collector.
国内没有一个动物园报告丢失了美洲狮，所以这头美洲狮一定是属于私人收养者的。
The gang was caught in possession of stolen goods.
这伙人被逮住，人赃俱获。《牛津高阶英汉双解词典》
The widow is in possession of a large fortune.
那个寡妇拥有大笔财产。
They have been in possession of the island for time immemorial.
他们自古以来就拥有该岛。
Anyone found in possession of this poison will be punished.
发现拥有此种毒品者将受到惩罚。
He was found in possession of dangerous drugs.
她被发现藏有危险药品。
My solicitor is now in possession of the documents
我的律师现在已经掌握了文件。
My mother-in-law is in possession of a large sum of money.
我丈母娘拥有一大笔钱。
At that time the Ford family was in possession of a large number of black slaves.
那时福特家族拥有大批黑人奴隶。
2. in the possession of= possessed by 由……来掌握；在……手里；归……所有
Those documents are now in the possession of the Guardian
那些文件目前在《卫报》手里。
The land is in the possession of the merchant.
这块地为该商人所有。
The house is in the possession of the Hunters.
这座房子是亨特一家的。
The old house is now in the possession of the government.
那栋老房子现在归政府所有。
Large fortune is in the possession of the woman.
大宗财产掌握在这个女人手里。
All the deeds are in the possession of my solicitor.
所有的契约都由我的律师来掌握。
The women slaves were in the possession of a cruel landlord.
那些女奴掌握在一个残酷的资本家手里。
常常用 in sb's possession 来替换in the possession of sb。例如:
The fort has been in our possession for some time.
那座城堡已被我们占领一些时候了。
3.take possession of占有，拥有，接收，获得；携带
You cannot legally take possession of the property until three weeks after the contract is signed.
契约签署三周以后，你才能合法取得这份产业的所有权。
We should go up and take possession of the land
我们应该北上占领那片土地。
We've taken possession of their house.
我们把他们的房子接收过来了。
They take possession of peace, of tranquility, of leisure; behold, they are content.
他们获得了安宁、平静、闲逸，心满意足了。
We need to take possession of all our belongings before we leave the hotel.
在离开酒店时我们必须携带好我们全部的物品。