Zhi Zhao, 62 operated the Grace Chinese takeaway on High Street, Cilgerran, despite being banned from running a food business in 2009.
At Swansea Crown Court, he admitted five food hygiene offences.
“If the public had seen the state of that kitchen then you would not have had a single customer,” Judge Geraint Walters said.
“It is hard to imagine anything quite so dirty.”
Mr Walters said the kitchen was “a dreadful mess, unspeakably dirty.”
Martha Smith-Higgins, prosecuting for Pembrokeshire council, said Zhao ran the takeaway “without having a basic understanding” of what was required.
Following an inspection in January 2018, council officials found he had been banned by Maidstone council in 2009 from being involved in food businesses.
Representing Zhao, Craig Jones said he had surrendered the lease and as far as he knew the business had closed.
He had been staying with a friend on Argyle Street, Swansea, working as a delivery man.
In sentencing, Mr Walters said Zhao had no concept of labelling food or keeping proper records and no understanding of allergens.
He called for a national register of banning orders so local authorities are aware of them.
Zhao admitted three food hygiene offences relating to the condition of the premises, one of failing to comply with a food safety improvement notice and one of running a food businesses after being banned by a crown court.
He was jailed for four months and ordered to pay £1,000 prosecution costs.