Received California 1099-g , the source of income is last year state income tax refund ， however there is not such source in turbo tax options

If it’s asking why you got a 1099G you are in the wrong place.  Delete out of this one.

To enter a state refund just type  1099-G (with the dash)  in the search box at the top of your return and click on Jump To it.

The amount is in box 2.  That is for a state refund you got in 2024 for your 2023 return.   It goes on your 2024 tax return.  But you might not need to enter it at all.

Enter the 1099G under

 Federal on left

Wages & Income

 Scroll down to 1099-Misc and  Other Common Income

     You might need click on Show More to expand the section

Then it's the first line for Refunds Received for State/Local Tax Returns - Click Start

     You do not want the next line that says Other 1099G Income

On the first screen check YES - Received a State Refund.

But you might not need to enter it at all.  

Is it for a state tax refund you got in 2024 for your 2023 or prior state return?  Is the amount in box 2?  You may not need to enter it.  Did you take the Standard Deduction on that year federal return?

A State Tax Refund is taxable if you itemized deductions on that prior year's federal return and took a deduction for state income taxes instead of the sale tax.  You got a deduction benefit for it so now you have to include it as income. If you took the standard deduction it is not taxable and you don't need to report it.

To enter a state or local tax refund (Form 1099-G) -

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)

Scroll down to Other Common Income
On Refunds Received for State/Local Tax Returns, click the start or update button

Or enter state refunds in the Search box located in the upper right of the program screen. Click on Jump to state refunds