The initiative is aimed at improving the public image of a force with a reputation for corruption and abuse.
Inspectors have been monitoring officers on duty to identify the worst offenders, state media said.
Several countries have taken action on overweight police in recent years as global obesity rates soar.
"Little officers or those with too big a belly will be moved to work in offices so they do not come into contact with the public," Hanoi traffic police chief Col Dao Vinh Tang said.
Overweight police officers will be required to undergo regular physical training.
In addition, all police on duty will be required to carry an official code of conduct to remind them how to behave, official newspaper Tien Phong reported.
It is the latest step taken to try to improve the image of Hanoi's traffic police force, which has faced frequent complaints as it manages the city's hectic flow of vehicles.
In 2011 officers were banned from wearing sunglasses or hiding behind trees to ambush unwary motorists and extract fines.
And in January, specially trained women police officers were deployed at key junctions to win over the public.
A World Bank survey of perceived corruption in Vietnam last year ranked traffic police as the worst offenders.
In recent years countries including the UK, Mexico and South Africa have introduced measures to help police officers lose weight, as expanding waistlines and reduced fitness hamper the fight against crime.
Traffic police officers who are short, obese or abusive are to be removed from the streets of Vietnam's capital Hanoi, local media reports say.