I'm 29 year old and I'm patient whit rheumatoid arthritis! The risk is big if I do a Tummy tuck?

As long as you are medically cleared for the tummy tuck, you should be fine.  It's important to notify the doctors of the meds you are taking as well to see if anything needs to be held beforehand.

Your overall health will be assessed by your plastic surgeon.  To further make the surgery safe, he or she may work with your specialist or general physician who will make sure that your condition is well under control prior to surgery. If you are taking anti-inflammatory and other meds known to affect normal bleeding and healing, the general rule of thumb is to avoid them three weeks prior to surgery. Make sure that you go to a board-certified plastic surgeon who mainly performs tummy tuck. Good luck. 

I do not think it will be an issue as long as your arthritis is in a stable position and your medication is not going to be changed. Immunosuppresant therapy can be continued after surgery and will not affect the result or recovery. Good luck.