if object_id('pro_test')is not null
drop proc pro_test
go
create proc pro_test @tblname varchar(20)
as
declare @str varchar(200)
set @str=
'if object_id('+quotename(@tblname,'''')+') is not null
 drop table '+@tblname
print @str
exec(@str)

--TRY

------解决方案--------------------
SQL code
if OBJECT_ID('test','P')is not null
drop proc test
go
create proc test
( 
   @table_name   varchar(max)
)
as
declare @sql varchar(max)
set @sql='' 
select @sql=@sql+'if object_id('+''''+@table_name+''''+') is not null drop table +'+@table_name+'+'+''

exec (@sql)