In order to improve the early diagnosis rate of Parkinson's disease (PD), reduce the complications of PD in the later stage, and make the clinical intervention to alleviate the pain of Parkinson's patients early, Magnetic resonance imaging (MRI), positron emission tomography (PET), and computerized tomography (CT) were used to evaluate the characteristics of PD. A total of 34 patients diagnosed with PD admitted to Qilu Hospital of Shandong University from January 2017 to December 2018 were included in the research. According to the severity of the disease, the patients were divided into the initial group (IG) (22 cases) and the latter group (LG) (12 cases). MRI, PET, and CT were used to scan the patient's brain to obtain different scan images. The obtained image was processed to improve the image resolution. Brain MRI and CT images were registered. The processed MRI and PET images were segmented to obtain the corresponding caudate nucleus (CN) segmented images. The complete CN volume of patients was obtained from the pixel points and compared with the calculated value of Pen G's Multifunctional Operative Dissector (PMOD). The accuracy of the established multimodal magnetic resonance (MMR) technique in the diagnosis of PD was determined by manual cutting (MC). The rate of CN lesion was calculated according to the formula to determine the correlation between PD and CN lesion. The results showed that MRI, PET and CT could successfully obtain brain images of patients. After processing, the sharpness of the picture increased, which was easy to observe and provided guarantee for follow-up experiments. Brain MRI and CT image registration can register brain images in different modes to the same space. MRI image can segment the complete CN, while PET image can segment the intact CN. Compared with MC, the probability of CN calculated by the formula had a small error, which could be ignored. The error value was less than the calculated value of PMOD. The rate of CN lesion in the IG was greatly lower than that in the LG (P < 0.05), which showed that the MRI, PET and CT combined multimodal MRI can be used to diagnose PD with a high rate of quasi-discontinuity, which provides a new technique for clinical diagnosis.