Hi Elham,
I presume you want to replicate material groups in ECC in SRM product categories (The terminology is different though). You can use the following steps once the material groups are created in ECC.
1 - T code R3AC3 and object DNL_CUST_PROD1. Here you can filter the material groups you want to replicate. Also you need to replicate both tables T023 and T023T.
2 - Load the object DNL_CUST_PROD1 via Tcode R3AS.
3 - You can monitor the replication via Tcode R3AM1.
Regards
MKK