在一家工厂用英语说为In a factory。
双语例句：
1、这种材料在一家工厂里用机器加工成型。
The material is machined in a factory?
《柯林斯高阶英汉双解学习词典》
2、后来他在一家工厂工作。
Later he worked in a factory.?
中考真题- 2017 天津 任务型阅读
3、他们一直在抗议一家氯工厂排放有毒气体。
They have been protesting about fumes from a chlorine factory.?
《柯林斯高阶英汉双解学习词典》
4、他们计划在东欧开办一家工厂。
They are planning to open a factory in Eastern Europe?
《柯林斯高阶英汉双解学习词典》
5、公司将在威尔士开一家新工厂。
The company are opening up a new factory in Wales.?
www.enread.com