Objective To investigate the correlation between serum migration inhibitory factor (MIF), brain-derived neurotrophic factor (BDNF) and urine Alzheimer-associated neuronal thread protein (AD7c-NTP) expression levels and cognitive impairment in patients with Parkinson's dementia. Methods From February 2018 to February 2020, 115 inpatients and outpatients with Parkinson's dementia in Ningde Hospital Affiliated to Fujian Medical University were enrolled as study group, meanwhile, another 118 healthy individual were enrolled as control group. Study group was further divided into three subgroups according to Mini-Mental State Examination (MMSE) scores, mild group, moderate group and severe group. Then the comparison of clinical data, fractional anisotropy (FA) and mean diffusivity (MD) in each region of interests, serum MIF, BDNF and urine AD7c-NTP levels was carried out within groups and subgroups. Results MMSE score of study group was significantly lower than that of control group (P＜0.05). Serum MIF and urine AD7c-NTP levels of study group were higher than those of control group, and serum BDNF level was lower than that of control group (P＜0.05). FA and MD values showed significant difference among three subgroups (P＜0.05). Serum MIF level and urine AD7c-NTP levels among three subgroups were the highest in severe group, followed by moderate group and mild group, with significant difference (P＜0.05). Serum BDNF level among three subgroups was the lowest in severe group, followed by moderate group and mild group, with significant difference (P＜0.05). Serum MIF level and urine AD7c-NTP levels were positively correlated with degrees of cognitive impairment (P＜0.05), and serum BDNF level was negatively correlated with degrees of cognitive impairment (P＜0.05). Conclusion Degrees of cognitive impairment in patients with Parkinson's dementia are positively correlated with serum MIF and urine AD7c-NTP levels, and negatively correlated with serum BDNF level, so patients with elevated serum MIF and urine AD7c-NTP levels as well as decreased serum BDNF level suffer a more severe cognitive impairment, thus the three can be used as important indicators to judge the cognitive impairment in patients with Parkinson's dementia, and provide a reference for the clinical treatment.