Abstract: On August 8,1998,the discharge of Qingjiang drai nage area was higher than that given by the standard of floodfrequency 0.1%,th en,the water level before Geheyan dam was 203.94m,i.e. 3.94m higher than norm al water level,so the storage of flood volume played a great role in the flood p revention downstream of Yangtze River.In the analysis of deformation monitoring data in 1998,taking three transveral lines(through dam crest level 206m,dam body level 145m and dam foundation,respectively)and four vertical lines(through the right arch abutment of dam section No.10,the arch crown of dam section No.15 ,the left arch abutment of dam section No.21 and the gravity pier of dam section 26,respectively) as analytic paths,the analyses of characteristic values for th e measured points of large deformation quantity were made using physical rationa l method;aiming at the monitoring data with the type of multipeak curves ,a de formation model was established using step by step regression method,which conta ins general linear polynomial expressions;at last ,a preliminary analysis on dam working status was done.