Objective To explore the brain mechanism of arousal abnormal in emotional processing in abstinent heroin abstainer.Methods Totally 13 heroin abstainers(experimental group) and 13 healthy subjects(control group) underwent fMRI when viewing pictures with different arousal levels.Then the arousal ratings were evaluated by the subjects.fMRI data were processed with AFNI software.Behavioral data were analyzed with SPSS 13.0 software.Results Looking at emotional pictures,compared with control subjects,brain activation of experimental group decreased in left amygdale and hippocampus,bilateral thalamus,cingulate gyrus,bilateral superior frontal gyrus and middle frontal gyrus,right precentral gyrus,bilateral superior temporal gyrus,right inferior tempotal gyrus,left fusiform gyrus and bilateral caudate nucleus.ROI analysis indicated increased brain activation in experimental group when watching high arousal stimuli than low arousal stimuli in right thalamus,left amygdale and hippocampus,while the controls showed the opposite pattern.Conclusion Heroin abusers have abnormalities in arousal processing.