The Police Investigations and Review Commissioner (PIRC) said the incident, at a firearms range in Dumfries, could have been prevented.
The police officer, who was also the designated safety officer, was “slightly injured” when the weapon went off as he tried to return it to the holster.
He required hospital treatment when the electrodes from the Taser shot into his finger at the range, within the Cornwall Mount police station in Dumfries in May this year.
Widely used by Scotland’s police, Tasers fire small darts which incapacitate using an electric shock.
In a report released yesterday, the commissioner, Kate Frame, made a series of recommendations, including calling for the holster in use to be withdrawn.
According to the officer involved, the Taser may have gone off either when a fastener on the holster caught the trigger or when his trigger finger was forced back by the cover of the holster.
A forensic examination of the holster found that moving the Taser in and out of the holster could result in the safety catch being moved from the “on” to the “off” position.
Ms Frame said: “Forensic examination determined that the scenarios described in the statements provided cannot be discounted and both are feasible reasons for the unintentional discharge of the Taser.
“Although preventable, the fault cannot sit entirely with the operator in this incident as the design of the Taser holster itself predicates an accidental discharge. To prevent further similar incidents, I hope that Police Scotland will act quickly on my recommendation that they stop using this type of holster.”
The PIRC’s investigation uncovered concerns among firearms officers over the use of the holster, although there was no record of an officer making a formal report.
The commissioner’s report also recommended that a safety officer be observed by other safety officers when carrying out function checks and load/unload drills.
She also called on Police Scotland to stress to its officers the importance of “scene management” at firearms incidents, leaving unintentionally discharged weapons untouched and neither loading nor unloading them.
Chief Superintendent Elaine Ferguson said: “Police Scotland note the findings of this report, including the recognition that if accepted practice and procedures had been fully adhered to, it would not have occurred.
“The recommendations, some of which have already been addressed, will be considered fully and, where appropriate, will be acted upon.
“In respect of the procurement and roll-out of replacement holsters, this process is already in progress and will be completed shortly.”
The PIRC is currently investigating another incident during which a man wielding a knife was shot with a Taser on Princes Street, Edinburgh, in July.
During the incident, a police officer was injured and required hospital treatment.