The Shots have taken just seven points from their last seven matches and although they are sitting 20th in League Two, they are only two points above the relegation zone.
A club statement read: "Despite Tuesday evening's hard-fought result against Torquay (a 1-0 win) the board of directors have taken the decision to terminate the contract of first-team manager Dean Holdsworth with immediate effect.
"The board would like to place on record their thanks and appreciation for Dean's efforts during his time at the football club and acknowledge the difficult circumstances under which Dean has managed to steer us out of the relegation places.
"Dean also leaves as a Football League manager with the club remaining in Football League status.
"However, despite this and taking into account our current league position and game in hand of those teams around us, the board felt the time was right to maximise the positive momentum of Tuesday's result in order to give the best possible chance of retaining our League status.
"With this in mind and just 13 games left of the season we must now move quickly and make every effort to find a suitable replacement that can help us achieve those immediate ambitions.
"We understand the time-sensitive nature of any discussions and hope to be able to confirm the position prior to Saturday's home fixture against Fleetwood at the EBB Stadium."