Three serious jam accidents occurred to TBM when boring in parallel adit of Gaoligongshan Tunnel on DaliRuili Railway in fault and fractured zone. In order to reduce the construction risk, speed up the construction schedule and save the construction cost, the causes for cutterhead jam are analyzed, and the necessity and feasibility of shield extension are studied by means of investigation, engineering analogy and expert argumentation; and then, the shield extension scheme is developed, i.e. the space between shield and cutterhead is shorten from 360 mm to 50 mm. The practices show that under the proportion of grade Ⅳ and Ⅴ surrounding rocks reaching 67%, jamming accident does not occur when TBM continues to tunneling about 1 500 m, the tunneling efficiency is improved greatly and the effect of shield extension is remarkable.