ALTER procedure [dbo].[cs2]
@a nvarchar(100),
@b nvarchar(100),
@c nvarchar(100)
as
declare @d nvarchar(2000)
set @d=N'select * from '+'i_'+@a+' where iname='''+@b+''' and ipassword='''+@c+''' '
execute sp_executesql @d

------解决方案--------------------

似乎是要从若干个表中按参数@a选择某个表进行查询，条件为iname=@b, ipassword=@c?
建议预先建立视图将若干需要查询的表数据整合：
create view vw_tb_name_passwd as
select tbname='tb_a', iname=iname, ipassword=ipassword
from tb_a
union
select tbname='tb_b', iname=iname, ipassword=ipassword
from tb_b
..
然后基于此视图进行查询：

ALTER procedure [dbo].[cs2]
@a nvarchar(100),
@b nvarchar(100),
@c nvarchar(100)
as
 select *  
 from vw_tb_name_passwd
 where 1=1
 and tbname = @a
 and iname = @b
 and ipassword=@c