Hi,i have managed to find out how to set different banner on multistore.I'll post the steps here for people who would like to set different banner :
AbanteCart cart different banner on each store :
1. Create new group in banner manager
2. Assign Banner to Banner group
3. Create new block
4. Select banner block
5. Use block wrapper : blocks/banner_block/one_by_one_slider_banner_block.tpl
6. Click on selected banners on the create banner block,select the banner you just create and apply
7. set the new created banner block on the layout
8. enable the block from the block manager
9. That's it