Le Phu Cao, 32, was arrested from a hiding place in Lien Chieu District.
He is believed to have got away with more than VND600 million (US$25,540) from the bank at around 11 a.m. on Thursday.
The Da Nang police said he refused to talk at first before later agreeing to show them where he hid the money.
They said he used a motorbike with a fake license plate for the heist.
He rode up to the bank, went inside and locked the door behind him.
There were five employees and a security guard inside. The security guard said the robber wore black clothes, had a gun in one hand and an electric baton in the other, threatened the guard, and asked the employees to put money inside plastic bags.
The entire robbery took just a minute.
Passers-by said the suspect rode a gray Yamaha Grande motorbike, recorded the license plate and sent it to the police.
No one was harmed during the robbery.
The bank is in downtown Da Nang, 800 m from the city police headquarters.