已解决：
class InfoAdmin(admin.ModelAdmin):
search_fields = ['title']
list_display = ('title', 'publish_time')
list_filter = ['tags', 'publish_time']
fields = ['title', 'content', 'publish_time', 'tags']
filter_horizontal = ('tags',)
def save_related(self, request, form, *args, **kwargs):
super(InfoAdmin, self).save_related(request, form, *args, **kwargs)
tags = form.cleaned_data.pop('tags', ())
info = form.instance
for tag in tags:
tr = TagRelate.objects.get(tag=tag, info=info)
tr.info_publishe_time = info.publish_time
tr.category_id = tag.category.id
tr.save()
