Objective To investigate the relationship among the D-dimer,C-reactive protein and left atrial diameter in the patients with atrial fibrillation(AF). Methods 53 AF patients were selected,the control group consisted of 32 cases of sinus rhythm(SR). The levels of D-dimer, CRP and LAD in AF group were compared with each other, and with those in the control group. Correlation analysis between D-dimer, CRP and LAD were made.Results D-dimer,CUP and LAD in AF group were significantly different from those in SR group. D-dimer and CRP in persistent AF and permanent AF differed significantly from that in SR and paraxymal AF. LAD in the group of persistent AF differed from that in SR group. LAD in permanent AF was significantly different from that in paraxymal AF and SR. Positive linear correlations were found between D-dimer, CRP and LAD in AF (r=0.376; 0.33).Conclusion Hypercoagulable state existsed in AF; the elevation of CRP should be the result and related to persistence time of AF. Positive correlation existsed between LAD and hypercoagulable state and inflammatory reaction.