A man a armed with a handgun, hammer and an umbrella demanded money from staff at the Tesco Express in Furzton on March 17.
At around 9pm the man approached two female members staff and demanded they opened the tills.
He grabbed cash from out of the tills and left the store, a quantity of money was stolen during the incident.
The offender is described as white, approximately 5ft 8ins, slim, aged in his early twenties, with brown hair and brown eyes.
He was wearing all black clothing and had his head covered with a black hooded top.
He was carrying what appeared to be a black handgun, a black umbrella which appeared to be wind-damaged, and a hammer which had a black handle.
Investigating officer Det Con Lucy Jarrett said: “I would like to speak to anyone who has any information about the robbery.
“Thankfully no one was hurt however it was a worrying experience for the members of staff.
“Detectives are working to identify and locate the offenders. I would also like to speak to anyone who saw anyone acting suspiciously in the area at the time of the incident.”
Anyone with any information about the incident should contact the 24-hour Thames Valley Police enquiry centre on 101.
If you have any information relating to this case, please call 101 quoting reference ‘43170079040’, or contact Crimestoppers anonymously.