Something or someone that is indispensable is so good or important that you could not manage without it, him, or her.

This book is an indispensable resource for researchers. 这本书是研究者必不可少的资料。

His long experience at the United Nations makes him indispensable to the talks. 在联合国长期的工作经验使他成为谈判中不可或缺的人物。