I'm receiving a small backpay for ssi disability,and I owe the IRS,will they take my disability?

They can - I don't know if they will. Tax liabilities are one of the few debts that can be taken from SS.

We cannot say for sure without knowing your overall financial situation.

If the SSDI backpay is badly needed to handle costs that must be paid to maintain your health or standard of living, then the IRS garnishment can be successfully challenged. Otherwise, the IRS will garnish it.