Bulk import/update of N-N relationship data

Hello,

Here is my scenario.

I have created custom entity called "industry Group" and prepared a master of the same. My each account is falling into diff and more than one industry group which i want to manage in crm.

I have added sub grid in to account form to link more than one industry group into account. 

Now i want to upload industry group in Sub grid of account(entity) form . 

Is there any way to import industry group in bulk.

Please suggest me a suitable solution for this.

Thanks in Advance