Abstract: Objective To investigate the diagnostic consistency of chest CT pre-operation and pathology post-operation of mediastinal lymph node metastasis in lung adenocarcinoma， in order to offer the basis for delineating target area. Methods From Jan. 2009 to Nov. 2011， 107 patients of lung adenocarcinoma were enrolled in this study. The size and number of mediastinal lymph nodes scanned by chest CT and diagnosed by pathology were analyzed， and the rate of metastasis was calculated. Results The metastasis rate of length ＜15mm detected by chest CT was 26.8％， and the rate of length ≥15mm detected by chest CT was 72.6％. With the increasing of lymph node number detected by CT and lymph node diameter, the metastasis rate raised. Conclusion With the increase of lymph node length， the metastasis rate is increasing gradually. The metastasis rate is higher in lymph nodes＞2 than in ≤2， even in smaller length of lymph node.