Citizens of Iran can apply for a visa to Vietnam in 2 different ways:
1. Apply for a Vietnam visa in person at the nearest embassy of Vietnam in Iran. Kindly be advised that the procedures and fees are subject to be changed depending on where you apply. If there is no consulate/embassy of Vietnam in Iran, there may be a embassy of Vietnam in neighboring countries of Iran.
2. Visitors can also apply for a visa on arrival to Vietnam from Iran. First, the online application form needs to be filled out. After 2-3 business days, an approval letter will be issued, scanned and emailed to the applicants.
You want check service fee for citizen Iran at : Vietnam visa service fee for citizen Iran