The utility model discloses a hydraulic jar belongs to the oilfield machine field. This hydraulic jar includes: the top connection that from top to bottom feeds through in order, outer barrel, lower clutch, outer barrel includes: the path inner chamber section and the big footpath inner chamber section that communicate from top to bottom, the last jarring body that links to each other and the jarring body down, but that the urceolus is located to equal endwise slip ground cover is internal, and go up the jarring body the upper end, down the jarring lower extreme of personally experiencing sth.Part of the body be used for jarring top connection and lower clutch respectively, sealing member, suit are under on the jarring body for annular gap under the movive seal between the jarring body and the path inner chamber section, and the external diameter of sealing member is less than the internal diameter of big footpath inner chamber section, go up the elastic component, set up the intracavity of exerting pressure that forms in the last jarring body and path inner chamber section, and upper and lower end respectively with top connection and jarring body counterbalance down, lower elastic component sets up in the jarring body down and pressure relief cavity that the urceolus bodily form becomes, and upper and lower end respectively with the jarring body and lower clutch counterbalance down, be provided with intercommunication pressure relief cavity's pressure release hole on the wall of big footpath inner chamber section.