I am going to China in August, I want to book a flight ticket online. The summer ticket is very hot, thus it is hard to get. I don't know the exact date to depart USA until next week. Can I book one in advance? Which means I hold it and confirm it next week?
The specific policy will depend on your fare rules and on the airline you choose, but a week is a frightfully long time when it comes to airline tickets.
Some airlines let you pay a fee to reserve a seat and guarantee the price at the time of booking for up to seven days. For example, United calls its offering FareLock, Air France Time to Think, and Lufthansa the unimaginative flight reservation with price guarantee. It may not be offered for every fare or on every route.
Some airlines allow you to reserve the seat and price for free, but only for 24 hours after booking or till midnight the following day. Some airlines, including American, make it possible to hold online; others require you to call in.
Still other airlines, including Qantas, allow you to reserve a seat for free, but will not honor the price at reservation time.
Among U.S.-based airlines, it is most common now that the airline will not hold a reservation for you; however, they do give you up to 24 hours to cancel a purchase without penalty, subject to other restrictions (e.g. the trip might need to be at least a week or two in the future). In other words, you have post-purchase rather than pre-purchase flexibility. In my experience, the refund extends even to non-refundable fares.
Cathay Pacific, for its part, allows either a 24-hour prepurchase hold or a 24-hour postpurchase refund grace period, but not both.
Things are a looser with frequent flyer award tickets— sometimes. Air Canada, British Airways, and others do not allow holds on award tickets at all, and few airlines are willing or able to hold award seats on partner carriers. But if you are redeeming on your "native" metal, you may be able to call in and hold the seat for several days.
Extending a hold
Sometimes, you can get call in and get an agent to extend a hold for you once or twice, especially if you have elite frequent flyer status. But there are no guarantees. They will not do so on high-demand routes, especially for frequent flyer redemptions in premium cabins, and may not be able to enforce a hold or an extension of a hold on partner airlines in the itinerary in the first place.
Back in the days when many bookings were done through travel agents and on paper, there was more uncertainty as well as more capacity, allowing holds of three or even seven days on some fares. But airlines, like any other business, prefer to have the revenue of someone willing to pay now as opposed to the potential revenue of someone who might pay later, and in the modern competitive environment, holds are quite unpopular. The 24-hour window persists because ARC, the largest clearinghouse for airline tickets, continues to extend its traditional 24-hour grace period for travel agents to void tickets without penalty— but that may not last either.