1、词性上的区别
their是形容词物主代词，后面可以接名词。
theirs是名词性物主代词，后面不能接名词。
2、意思上的区别
their：他（她，它）们的
theirs：他们的; 他的或她的。
造句：
①、their
It would cost about £ 3,000 to install a new heating system in a flat such as theirs
在他们那样的一套公寓房里安装一套新的供暖系统可能要花费3,000英镑左右。
Theirs had been a happy and satisfactory marriage.
他们的婚姻曾经一直幸福美满。
②、theirs
There was a big group of a dozen people at the table next to theirs
他们旁边的桌上坐了一大群人，有十几个。
This child is nobody's child until someone makes her theirs officially.
在有人办理正式手续认领以前，这个孩子不属于任何人。
