Think of your visa as a key to your house. It allows you to open the door.
The visa stamp in your passport may expire while you stay in the U.S., but the visa must be valid whenever you re-enter the U.S.
A valid visa is not necessary when returning from Canada, Mexico and most Caribbean islands if you have been gone for less time than 30 days. This exception does not apply to students from North Korea, Cuba, Syria, Sudan, Iraq, Iran and Libya.
When you re-enter the U.S. from abroad (except for above exceptions), your visa must:
List your current visa status.
Not have expired.
Have additional entries remaining. "M" means that you can enter multiple times in that visa status.
Visa renewal process
If your visa has expired or you have used all of the entries, you must have it renewed at a U.S. embassy or consulate in your home country or another country. You cannot renew a U.S. visa inside the United States.
If you renew your visa in a country other than your home country, please make an appointment to discuss your plans with an international student adviser.
Some applicants will also be required to complete and sign Form DS-157.
Blank forms are available without charge at all U.S. consular offices and on the Visa Services site.
A receipt for the visa application fee showing payment for each applicant, including each child listed in the passport of a parent who is also applying for a U.S. visa.
An I-20 or DS-2019 that has been signed for travel by an international student adviser within the past 12 months.
Student visa applicants must establish to the satisfaction of the consular officer that they:
Have binding ties to a residence in a foreign country, which they have no intention of abandoning.
Will depart the U.S. when they have completed their studies.
It is impossible to specify the exact form the evidence should take since applicants' circumstances vary greatly.
Additional information:
Please check the website of the U.S. embassy or consulate to which you will go to find out whether additional documents are required. You must submit these documents to the embassy or consulate.