Most studies have focused on comparing blood lipid biomarkers between Parkinson's disease (PD) and normal controls (NC). However, further research is necessary to explore the impact of blood lipid levels on motor and cognitive function, as well as the progression of motor dysfunction and cognitive decline over time. Thus, the aim of this study is to investigate the relationship between blood lipid biomarkers and these indicators in individuals with PD. The cohort study enrolled 157 PD patients and 146 NC from the Tianjin Huanhu Hospital from September 2017 to September 2019. Serum lipid fractions were detected in fasting serum samples. PD patients were followed up at 2 ± 0.6 years for clinical assessment. PD patients exhibited lower serum triglyceride (TG) levels as compared to NC (P = 0.008). PD male patients exhibited lower serum lipoprotein cholesterol(LDL-C) and total cholesterol (TC) levels than female patients (LDL-C: P = 0.034; TC: P = 0.019). Serum TG levels correlated significantly with Unified PD Rating Scale III, Hoehn and Yahr stage and Montreal Cognitive Assessment scores in PD patients. Additionally, serum TG levels were associated with follow-up motor function decline and cognitive decline in adjusted regression models in PD patients. To summarise, the study findings suggest that decreased serum TG levels are significantly associated with greater motor dysfunction, cognitive dysfunction and the greater deterioration of the two indicators.