You can work while getting SSDI as long as you follow the rules and your income is not too high.
Trial Work Period:
When you first start working, you get a trial work period. During the trial period, you get full SSDI benefits no matter how much you earn. In 2013, each month that you earn $750 or more counts as a trial work month. After nine trial work months, your trial work period ends. The months do not have to be consecutive.
Note: The amount of monthly income that counts as a trial work month changes each year. See Trial Work Period Increases.
Extended Period of Eligibility:
Once your trial work period is up, you get 36 more months when you can work and still get SSDI benefits. These 36 months are called the extended period of eligibility, or EPE. During the EPE, you get SSDI benefits each month unless your earnings for that month are "substantial."
In 2013, gross monthly earnings of $1040 or more ($1740 if you are blind) are considered "substantial." This dollar amount is referred to as the SGA ("Substantial Gainful Activity"). If you have work expenses related to your disability, you may deduct them from your gross earnings.
Note: The definition of "substantial" earnings changes from year to year. See Substantial Gainful Activity Increases.
After the EPE:
After the extended period of eligibility, you lose your SSDI benefits if you earn more than the SGA in any month. If that happens, you get "grace period" benefits for three more months, but then your SSDI benefits stop. Social Security will no longer consider you disabled.