I live in MA and part of my income was from CA during 2018. I filed CA tax return as a non resident and am wondering if I can get credit in MA.

Yes.  Since you are a MA resident, Massachusetts is allowed to tax all of your income, and California taxes the income you earned in California.  The purpose of the credit for taxes paid to another state is to reduce the effect of double-taxation, and your situation qualifies you to claim this credit.

Thanks for you reply. Then, In this case where I got refunded from CA tax return, What should I put for the question, "Enter the income tax paid on this income to Other States while you were a resident of MA.

Subtract the refund you received from California from the amount of tax that was withheld to California in the first place.  That net amount is what California taxed your income.  If California gave you a full refund, then you won't get any credit on the MA return, because you would in essence not have been taxed in California

Thanks for the clarification.

You are welcome.

To make sure, the amount of that was withheld to CA includes (2.Federal tax withheld+4. Social Sec. tax withheld+6.Medical tax withheld+17.State income tax) in W2? What if I have two State income tax (MA, CA) in W2 Line17?

No.  What was withheld to CA was what appears in Box 17 of the CA line.  The other amounts are the Federal Taxes withheld, Social Security Taxes withheld, and Medicare taxes withheld.  Those amounts went to those specific places, not California.