Objective:To investigate the alterations in brain dynamic functional network connectivity (dFNC) and their significance in Parkinson's disease (PD) patients with postural instability/gait difficulty (PIGD).Methods:Ninety PD patients admitted to Department of Neurology, First Affiliated Hospital of Nanjing Medical University from May 2016 to August 2019 were recruited, and 54 healthy controls matched with gender and age were chosen; their clinical data and resting-state functional MRI (rs-fMRI) data were collected. PD patients were divided into PD with PIGD (PD-PIGD) group ( n=49) and PD without PIGD (PD-non-PIGD) group ( n=41) according to Unified Parkinson's Disease Rating Scale (UPDRS) scores. Independent component analysis (ICA), sliding window method and k-means clustering were used to analyze the dFNC and compare among groups. Correlations of dFNC alterations with clinical scales were verified by partial correlation analysis. Results:Four repeated recurring functional connectivity states were identified, and PD-PIGD patients had high frequency in state 3 (44%) and state 2 (23%) of the low dFNC. In terms of dFNC time attributes, PD-PIGD patients had longer mean dwell time in state 3 than PD-non-PIGD patients and had lower number of transitions in state 3 than PD-non-PIGD patients and healthy controls, with significant differences ( P<0.05); PD-PIGD patients had significantly higher fractional windows and statistically longer mean dwell time in state 2 than healthy controls ( P<0.05). In terms of dFNC strengths, compared with healthy controls, PD-PIGD patients showed significantly decreased functional connectivity within default mode network (DMN, between medial superior frontal gyrus and precuneus) and auditory network (AN, between superior temporal gyrus and middle temporal gyrus), but significantly increased functional connectivity between sensorimotor network (SMN, supplementary motor area) and DMN (precuneus) in state 2 ( P<0.05, false discovery rate [FDR]-corrected). Partial correlation analysis indicated positive correlation between mean dwell time in state 3 and PIGD scores in PD-PIGD patients ( r=0.450, P=0.039). Conclusion:PD-PIGD patients exhibit specific dFNC, mainly characterized by low connectivity of the brain functional network and prolonged dwell time; local functional network domains often separate between DMN, AN and SMN networks and within the networks.