Laurence Vonderdell, 50, has been given a 14-month-sentence after convincing staff at a Barclays bank in Bournemouth that the fruit was a gun and telling them: "This is a stick up, give me the cash".
Vonderdell escaped with £1,100 in £20 bank notes however soon approached two police officers and immediately confessed to the crime.
Jailing him Judge Robert Pawson said: "He's gone into a bank with a banana in a plastic bag. It sounds laughable but the cashier didn't know that.
"What would have happened if an armed response unit had been called?"
Detective Constable Andy Hale added: "Even though the defendant handed himself in shortly after this incident and the cash was recovered, this must still have been a very distressing incident for the cashier involved."