之前看到有帖子讨论过，最后也没有答案。今天上网查到这个，应该是官方准确答案，给大家参考：
http://travel.state.gov/visa/temp/types/types_1262.html#notravel
Schedule an Interview
While interviews are generally not required for applicants of certain ages outlined below, consular officers have the discretion to require an interview of any applicant, regardless of age.
If you are age:Than an interview is:
13 and younger Generally not required
14-79 Required (some exceptions for renewals)
80 and older Generally not required
You must schedule an appointment for your visa interview, generally, at the U.S. embassy or consulate in the country where you live. You may schedule your interview at any U.S. embassy or consulate, but be aware that it may be difficult to qualify for a visa outside of your place of permanent residence.
Wait times for interview appointments vary by location, season, and visa category, so you should apply for your visa early. Review the
interview wait time for the location where you will apply.
