If you claim your parent as dependent and your 70 yrs old parent on social security and won $1000 dollars in lottery, does your parent need to file income tax?

In general, your parent would be required to file their own tax return for taxable income in their own name, even if they are your dependent.  However, if their only income is social security plus a $1000 prize, it is less than the threshold and they don't have to file a federal return.  You would have to check your state to see if a state return is required. 

For a person on non-taxable social security, they normally do not need to fill a return unless claiming a credit for example; or have more income like lottery winnings. Even though they may have to file a return you can still claim them, if their total income minus social security is $4,400 or less for the 2022 tax year; and of course you provide more than half of their support. 

The following rules apply to casual gamblers who aren't in the trade or business of gambling. Gambling winnings are fully taxable and you must report the income on your tax return. Gambling income includes but isn't limited to winnings from lotteries, raffles, horse races, and casinos. It includes cash winnings and the fair market value of prizes, such as cars and trips.

See Topic No. 419 for more guidance from the IRS.

Also, see TurboTax article on Gambling and Lottery winnings and reporting information.

As @Opus17 stated in general terms it will most likely not even be taxable if that is their only income for the year including social security. Be sure to report from their 1099-SSA, for social security benefits even if you believe they are not taxable. 

@maguila8586 

EDITED 01/25/2023 | 05:47 PM PST