Before you decide to strip the covers off of you mattress and search for holes, know that no air mattress holds air indefinitely. You will naturally have to re-inflate your mattress whether or not you have a leak.  Cold air, for example, causes your mattress to shrink. As the house cools down at night, your air mattress will likely soften a bit as the air cools. A space heater by the mattress can prevent this problem. Air mattresses need to “stretch” after they are bought. Don’t be alarmed if they feel soft shortly after you inflate them the first few times, they will quickly adapt. If, after several minutes, it is severely deflated, then you likely have a leak. Sit on the mattress after you blow it up – it should not sink more than 1-2 inches under your weight.  If you are still not sure if there is a leak, leave your mattress inflated overnight and put weight on it, like several textbooks. If it is more than a little deflated in the morning, you have a leak.  Keep the mattress inflated as you search for the leak. If you feel the mattress becoming soft, reinflate it before you start searching again. The higher the air pressure inside the mattress the more forceful the leak will be, making it easier to notice. Hold your hand over the valve and feel for any escaping air. It is usually located right next to the air pump and looks like a plug that you can detach to quickly deflate the mattress. Unfortunately, the valve is the one part of the mattress that is difficult to repair at home. If your valve is broken or leaky, call the manufacturer to order a replacement. The majority of punctures and leaks occur on the bottom of the air mattress after people accidentally leave things underneath the bed. Make sure the bed is fully inflated and then stand the mattress up on its side to examine the bottom. You want enough room to flip, turn, and move around the mattress to easily search for leaks. Slowly move your ear across the entire surface of the mattress, keeping your ear close enough to hear escaping air. When you...

TL;DR in Chinese:
充气床垫漏气是很自然的现象。 充满气后测试床垫是否漏气。 检查充气阀门。 为了找到漏气的部位，把床垫立起来放在一个安静、宽敞的房间里。 把头凑近床垫，让耳朵和床垫的距离保持在5到8cm之间。 不停地用打湿的手背感受泄露的气体，直到找到漏气孔。 如果你仍然找不到漏气孔，试试泡泡水检测法。 用普通笔或锐意笔把漏气的地方圈起来。 放掉床垫里的空气，并将床垫彻底晒干。