--try
select a.顾客编号,sum(b.订单金额) 订单金额
from tb_aj001 a,tb_aj002 b
where a.订单号=b.订单号
--and b.订单时间 between  ... and ...
--and b.订单状态=...
having sum(b.订单金额)>500
and count(a.订单号)>1
group by a.顾客编号;

------解决方案--------------------

SQL code
WITH t1 AS(
SELECT 'D001' oderno,'C01' cuno FROM dual 
UNION ALL
SELECT 'D002','C02' FROM dual
UNION ALL           
SELECT 'D003','C01' FROM dual
),t2 AS(
SELECT 'D001' oderno,90 odamt,'Finish' status,'20120601' txdat FROM dual
UNION ALL 
SELECT 'D002',600,'Finish','20120602' FROM dual
UNION ALL 
SELECT 'D003',450,'Finish','20120602' FROM dual
)
SELECT t1.cuno,Sum(t2.odamt)odamt FROM t1,t2 WHERE t1.oderno=t2.oderno GROUP BY t1.cuno HAVING Count(t1.cuno)>1 AND Sum(t2.odamt)>500