celery beat not working, but celery worker --beat is working, when use database

Celery 3.1.11

settings.py

# Celery transport
BROKER_URL = 'django://'
CELERY_ACCEPT_CONTENT = ['json']
CELERY_TASK_SERIALIZER = 'json'
from celery.schedules import crontab

CELERYBEAT_SCHEDULE = {
        'every-minute': {
            'task': 'tasks.sync_oracle_history',
            'schedule': crontab(minute='*/1'),
            },
        }

in project.apps.proj folder, add a tasks.py

from __future__ import absolute_import
from celery import task

@task(name='tasks.sync_oracle_history')
def sync_oracle_history():
    print "="*30
    print "TODO: sync_oracle_history pending"

no idea, any hints for me is welcome.

in bash shell,when run command: celery beat -A proj -l info, only send to queue, not runing the task,
but change the command celery worker -A proj -l info, the task will trigger.