Abstract: Objective：To evaluate the value of susceptibility-weighted imaging(SWI) in diagnosis of Parkinson disease (PD) and assessment of disease severity. Methods：Totally 30 PD patients and 30 healthy volunteers underwent SWI. The phase values of nuclei in extracorticospinal tract were measured and compared between PD patients and healthy subjects. Results：The phase values of sustantia nigra pars compacta, globus pallidus, putamen in PD group were all significantly lower than those in control group(P<0.01). The phase values of sustantia nigra pars compacta, globus pallidus and putamen reduced at the early stage in PD group, and then further reduced along with the severity of disease(P<0.05). Conclusions：SWI has important clinical value in diagnosing PD and evaluating the disease severity.