Would a petty theft charge affect me from getting my us citizenship?

I'll give you the typical attorney answer of "it depends". Were you convicted? What was your sentence? Have you had any prior convictions? If you haven't had any other trouble with the law, it probably won't negatively affect your citizenship efforts, but there is no way to know for sure based on the info you posted. It's best to contact an Immigration Attorney for a more in-depth analysis and consultation.