The robbery, in Sufton Street, Birkby, happened at about 1pm on April 26.
Five men forced their way into the shop after distracting the owner, who was then thrown to the floor during an altercation.
The group broke display cases using sledge hammers and filled large bags with jewellery before fleeing the scene.
They drove off from the scene in a white Ford Transit van which was displaying false registration places, a spokesman for West Yorkshire Police said.
The vehicle was seized by police after being found abandoned behind a row of shops nearby.
Officers believe the men then got into a cream or white-coloured car, and drove along Bradford Road.
The shop owner suffered minor injuries during the robbery.
The group were described as four Asian men, and one mixed race man.
Detective Constable Robert Brook, of Kirklees CID, said: “This was a frightening situation for the shopkeeper who was confronted by the suspects in the store.
“Fortunately, he sustained minor injuries during the incident, but was left very shaken.
“The suspects made off with a significant amount of jewellery worth around £20,000. I would like to appeal for witnesses who may have been in the area and may have seen the suspects or either of the vehicles near to the scene or driving away.
Anyone with information is asked to contact Kirklees CID via 101, quoting crime reference number 13180198331.
Information can also be reported to police via the Webchat facility on the West Yorkshire Police website or Crimestoppers anonymously on 0800 555 111.