The business's owner said the 36-year-old man had been employed by the pet salon since 2016 and had appeared "completely normal".
But the owner, surnamed Chen, said the employer had begun to change in the weeks leading up to the horrific incident in August last year.
The man allegedly took money from clients for services without the owner's knowledge.
Other staff members were shocked when Pan yanked the fluffy dog from its crate and began beating it with his sandal.
When his co-workers told him stop, he replied, "It was too noisy. It wouldn't stop barking the entire way here."
Fellow employees then rushed to check on the toy poodle, but Pan allegedly said, "There's no need to check. I've already beaten it to death."
Pan admitted to beating the puppy to death because he "lost control" of his emotions, reports said.
Authorities in Taiwan say the severity of the man's punishment would not be affected by his profession as a dog groomer or that he was the dog's legal owner.
