I got solution
go to base.css file and and below line:
.openerp_ie .oe_view_manager_buttons button .oe_form_button_duplicate {
padding-top: 0;
padding-bottom: 0;
}
go to view_form.js and add below line: line number 180
this.$buttons.on('click', '.oe_form_button_create',
this.guard_active(this.on_button_create));
this.$buttons.on('click', '.oe_form_button_edit',
this.guard_active(this.on_button_edit));
***this.$buttons.on('click', '.oe_form_button_duplicate',
this.guard_active(this.on_button_duplicate));***
this.$buttons.on('click', '.oe_form_button_save',
this.guard_active(this.on_button_save));
this.$buttons.on('click', '.oe_form_button_cancel',
this.guard_active(this.on_button_cancel));
we will get that button.
go to base.xml and add below line:
<button t-if="widget.is_action_enabled('create')"
type="button" class="oe_button oe_form_button_duplicate" >Duplicate</button>