There are services for mail forwarding. Some do international mail forwarding. If you are only going to be getting letters, there are some services that will send everything received once per month instead of instantly remailing each letter as it arrives. This is slower, but saves money.
There probably are even services that will open the mail, scan the contents, and email the scans to you. Alternatively, if you have a trusted friend or relative who has a scanner (a large percent of printers have one built in) and the amount of mail isn't too much, they might be willing to do this for free.
If you are completely out of touch with your parents and want your mail forwarded to USA address where some company or person will make arrangements to get messages to you, check USPS.com for instructions. Hopefully, you aren't Ivyman Smith, Jr. If you are, the post office will have a very hard time differentiating your mail from mail intended for Ivyman Smith, Sr. Note that postal forwarding orders are not forever, so as you finally get the mail (or scans of it), you need to notify the senders of your new US address. If you are getting some sort of financial statements (bank, retirement account, etc.), it should be possible to change to e-delivery. Regarding the IRS - Just keep them informed of your current Chinese address.