Please see the question I marked this duplicate of. For the specific transaction you referenced, we can see that one of the outputs has the same address as the input, so it should be somewhat obvious this is the change address, and the other output (0.015 BTC sent to 1Gdk...) is the 'payment'. Note that 'estimated BTC transacted' is a guess at best: in many cases, as an outside observer it is impossible to discern what the nature of a transaction's outputs are. – chytrik – 2018-10-23T02:45:42.067

Thanks! I have read How does blockchain.info calculate the “Estimated Transaction Value?” , but It's not clearly – HelloCW – 2018-10-23T03:20:50.397

Do you mean that "Estimated BTC Transacted displays 0.015B" is only a guess? – HelloCW – 2018-10-23T03:21:42.227

1I mean that when looking at a transaction, it is often not possible to know who controls each newly created output, and that info is needed in order to know 'how much bitcoin was transacted'. The 'Estimated BTC Transacted' statistic you can see on that page is simply blockchain.info's best guess at which output is the 'payment'. Sometimes, you can make a good guess, but often you cannot. – chytrik – 2018-10-23T04:31:48.927

Thanks! I'm strange why Bitcoin provide "Estimated BTC Transacted" and let users to guess! – HelloCW – 2018-10-23T05:20:09.090

Its not that bitcoin provides, it’s blockchaininfo calculations and not provided by bitcoin protocol, it is by design that one cannot know how much bitcoin is “spent” and how much returns as change. – Haddar Macdasi – 2018-10-23T06:12:54.653

@HelloCW the users involved in the transaction would not have to guess, because they will know who controls each output. But anyone else looking at the transaction will not have that information, and so they will have to guess. Blockchain.info is just a block explorer website, there are many such services that exist with similar websites. – chytrik – 2018-10-23T06:56:14.960