When I call url http://block-explorer.com/address/[my address] to see how many litecoin Received by that address, How do I know how many confirmations it has ?
On the front page of http://block-explorer.com, there will be a table, and the top number under "Block #" is the most recent block. On an address page, it will let you know the block number of the transaction that was sent to your address. If you subtract the two and add 1, you will get the number of confirmations.
Example: Suppose the most recent block is 12345. The transaction received by your address was included in block 12342. Then the number of confirmations is 12345 - 12342 + 1 = 4.
(Also, why the +1? Think about it: If the transaction is included in the most recent block, the difference between the two block numbers will be 0, but the number of confirmations is 1.)