I got the answer.
This Table Pool/Lazy Pool is to do with Nest Loop join. The query we did has a LOOP JOIN hint, which cause the Pool operation. Using HASH JOIN hint ( simply remove the hint, SQL Server pick up HASH JOIN) we did not see the Pool op., and executing time reduces by a fact of 18.
About the Table Pool/Lazy Pool, it means to copy inopput data to a temp spool table (for example, by a Nestd Loop operation). When rewinding, the spooled data is used instead rescan the table.