The jamming causes of 4 shield machines, used in Phase 2 project of Chongqing railway transit line 6, are analyzed in terms of equipment, geological conditions and construction. The countermeasures for shield machine jamming are summarized on basis of study on jamming releasing experiences in Chongqing area, so as avoid similar accidents and to guaranteed construction scheme, quality, safety and using life of equipment. The paper can provide references for similar projects in the future. 