Introduction: Bright light therapy (BLT) has been proved to have beneficial effects on Parkinson's disease (PD). Brainstem pathways improvements might be crucial to BLT, but the mechanisms remained unclear. The aim of this study is to validate whether BLT improves clinical symptoms in PD and thus explore the possible mechanisms of brainstem pathways evaluated by vestibular-evoked myogenic potentials (VEMPs). Methods: A total of 22 PD patients participated were enrolled in this crossover randomized placebo-controlled study. Participants received either one month of BLT or dim light therapy (DLT), separated by a 1-month wash-out period, and underwent clinical scales and VEMPs evaluations before and after each intervention. Mixed-effects regression models were used to determine the effect between BLT and DLT on PD patients by the differentials of clinical scales (Delta scales) and VEMPs (Delta VEMPs). Correlations between the improvement of clinical symptoms and VEMPs parameters improvements were analyzed in PD patients receiving BLT. Results: Excessive daytime sleepiness, anxiety, life quality and autonomic function were improved after BLT. Compared to DLT, the difference was not significant. There were significant differences of cervical VEMPs (cVEMP) and ocular VEMPs (oVEMP) peak latencies after BLT. Compared with DLT, there was significant difference in Delta Lp13, Delta Rp13 and Delta Lp11 peak latencies after BLT. Conclusions: BLT may be a valuable non-pharmacological intervention for improving brainstem function, thereby enhancing quality of life and overall health in PD patients.