这句话不对,因为在英文的句子中,一句话如果没有连词的话只能有一个谓语,就是动词,多一个动词就多一个连词,这句有很多种改法
可以加上一个连词：This is a school,and at the back of it is a mountain.
或者分成两句：This is a school.At the back of it is a mountain.
或者如果你学过定语从句的话,可以改成定语从句：This is a school,at the back of which is a mountain.
或者把两部分意议成一句：This school is at the back of a mountain.