Hi,I want to change my B2 Visa Status into F1 Visa. If my application rejected by USCIS than either it will effect my B2 Visa?,

No. Consult an attorney to draft a letter for you to exchange your visa

While the application is pending, you are in a period of stay authorized by the Attorney General. If the case is denied, theoretically, it is impossible to leave the US without incurring any overstay, partly because you cannot get the notice instantly. Thus, I think your B-2 visa should remain valid as long as you leave the US immediately. I had other people who did not have any problem in a similar situation. Since it's up to a CBP officer, however, you'd never know. Read from the bottom of the page six of 9 FAM (Foreign Affairs Manual) link below. http://www.state.gov/documents/organization/87498.pdf