Officers are also expected to protect other sites of worship throughout the country following a number of terror attacks across Europe.
In July two Islamic State militants slit the throat of Catholic Priest Fr Jacques Hamel, who was conducting Mass in a church in Normandy.
Last week a woman was also charged over a failed terror plot at Paris' Notre Dame Cathedral.
This will mark the first time that armed guards will regularly patrol the grounds of Canterbury Cathedral, according to The Daily Mail.
Critics have argued putting armed officers outside the cathedral will make the public feel less safe.
The increase in armed officers comes after the Home Office announced there would be around 1,500 more on patrol in England and Wales following a heightened terror threat.
In August Scotland Yard said London would have a further 600 armed officers protecting stations, Oxford Street, and places of worship.
