Getting a Chinese visa in Bangkok right now is a giant hassle. If you can do it literally else on the planet, do that. I've heard Chiang Mai is much more lenient, and I did it pretty easily in Vientiane about a year ago, but I guess I like a challenge. Here's all the info I gathered during the 5 days in Bangkok I spent getting all the ducks in a row:
Right now it's not possible to use an agent to turn in your passport for you, everyone has to go into the embassy themselves.
SO, when you get to the AA building, go in the door on the left side when you're facing the building, through a metal detector.
The lady at the door will want to look in your bags, and you can't bring any water or other drinks in.
Go up the stairs to the second floor, and when you get into the office, don't mess around with asking anyone questions or with the forms or any of that, go straight to the line with the red side that says "queue" to take a number. You'll be waiting for a long time, so get your number first, then go back to the desk at the entrance to get the visa application form.
It's the same form for tourist, work, or student visa.
If you're an American you need to fill out 2 of that form. Fill it out in all caps or they might not accept it.
Take your 2 passport photos and glue them onto the form yourself, they won't do it for you. There's a jar of glue on the counter where people are standing filling out forms in the back.
Wait 2-4 hours until your number comes up, and give them all the documents I'll list below along with a big cheesy smile and hope for the best.
And you need all of them.
I waited in that line 3 times in two days before they would even accept my documents.
You need
:The 2 visa application forms with photos glued on
:Printout flight confirmation from bangkok to china and back. In case you want to go in by train or are unsure of your dates, any of the travel agents around Khao San Road will make you a flight confirmation for about 500 baht/100 kuai, no problem
: Letter of employment from your current job saying that you work there and signed by someone, or if you're unemployed, you have to type up a quick note saying that you're unemployed and that you're going to China for travel and shopping and not to seek employment, and sign it.
: Printed, detailed itinerary of where you're going to visit while in China
: 2 copies of your passport info page
: Copy of your most recent Chinese visa
: Copy of your Thailand entry stamp
Plus either
1. A hotel booking confirmation and a copy of YOUR bank statement in your home country or in Thailand with at least 600 kuai for every day of your intended stay in China
or
2. An invitation letter from someone in China and a copy of THEIR bank statement.
If you go the invitation letter route, you must also have a copy of both sides of their ID card
The letter must include a sentence along the lines of "I will pay for all of your expenses during your stay in China" or "all expenses during your stay, including travel, accommodation, insurance, will be borne by me", or feel free to add your own personal flair.
The letter must also contain the inviter's name, phone number, and address (address in Chinese too) and YOUR passport number, and it must specify the dates of your intended stay in China.
Plus whatever other trifling little details they may feel like requiring that day.
When you pick it up, no need to take a number. Just go to the window on the far left to pay, then get your receipt and stand in line at the collection window to pick up your passport.