The Sky Blues have drawn all three of their matches in League One this season while they also won in the first round of the League Cup but that has not been deemed good enough by the club's board.
The cash-strapped Midlanders have conceded leads in all of their league games so far and Thorn has been punished with the loss of his job after the club also got relegated from the Championship last year.
Thorn took charge of Coventry in April 2011 following a spell as caretaker boss when former manager Aidy Boothroyd left the club.
He brought in nine new faces in the summer after the club's relegation and financial problems meant they lost key defenders Richard Keogh and Martin Cranie and young midfield star Gael Bigirimana.
The sacking continues a Coventry pattern of changing managers since the club were relegated from the Premier League in 2000.
Since that time Coventry have had 11 managers, with Thorn's 16 month tenure actually being one of the longest.