Members of the RMT union will walk out for 48 hours from 18:30 BST on 8 July.
The union said a guard should be kept on every train, "not a diluted customer service role", but First Great Western said having drivers controlling doors was safer and jobs would not be lost.
In the ballot, 80% supported strike action and 92% other forms of action.
The union said "no satisfactory solutions" had been proposed by management in response to its demands for a "safety competent guard" and buffet car facilities on trains.
It also said maintenance of the new rolling stock should remain in-house and there should be no job losses.
First Great Western (FGW) said it was seeking a meeting with the union following the ballot result.
A spokesman said: "We are disappointed that our assurances over job security, the need for more - not fewer - staff and maintaining existing pay and conditions for those staff have not been heard.
"These new trains will shave journey times by as much as 17 minutes, and provide the capacity we know our customers want to see but in order to be able to do this we need to operate these trains differently to the way we operate our current 40 year-old High Speed Trains.
"The best way to make the most of these new trains, in an efficient and safe way, is by the use of driver operation of the doors."
Buffet cars could also be replaced with a trolley service under the plans.
RMT General Secretary Mick Cash accused the company of "profiteering".
"RMT has made every effort to secure a series of very basic assurances from FGW over jobs, services and safety as a result of the introduction of the new Hitachi fleet and they have simply ignored us," he said.
The first Hitachi trains will run on the Great Western main line from 2017 and the East Coast main line from 2018.
The new trains are being introduced under the Intercity Express Programme (IEP) on routes between London Paddington and Oxford, Bristol and South Wales.
First Great Western rail workers have voted to support strike action over plans to axe guards and buffet cars on new Hitachi Inter City Express trains.