Research conclusions: ：(1)The engineering geological conditions in permafrost area along Qinghai—Tibet Railway are divided into four grades，namely good，general，poor and very poor．The corresponding measures for them are to adopt ordinary embankment，take a single active cooling measure，take two active cooling measures and build bridge．The safe running of train with 1 00 km／h on the Qinghai—Tibet Line in permafrost zone since open to traffic on July，2006 shows that the classification of engineering geological condition is feasible and the respective engineering structures are stable and reliable．(2)The cost of building bridge in very poor section Was 40 millions per kilometer，that was 4．4～15．4 times than the other section in the permafrost area．Therefore，railway route bypasses some very poor areas or passes it with the shortest distance．