Abstract： Objective To observe the differences in brain network activation and functional connectivity of patients with post-stroke cognitive impairment(PSCI)of different severity using functional near-infrared spectroscopy(fNIRS).Methods A total of 40 stroke patients in the outpatient and inpatient Rehabilitation Department in the Pudong District of Huashan Hospital,Fu-dan University from April to November 2020 were recruited and divided into normal group(n=14),mild to moderate group(n=11)and severe group(n=15)according to the mini-mental state examination(MMSE)score.Fugl-Meyer assessment scale(FMA)and functional comprehensive assessment(FCA)were used to evaluate the motor function of upper and lower limbs;64-channel fNIRS functional imaging device was used to collect the resting-state brain network data of patients.The whole brain functional connectivity was analyzed based on oxyhemoglobin(HbO2)and deoxyhemoglobin(HbR).Differences in functional connectivity strengths between homologous and heterologous brain networks in dorsal attention network(DAN),sensorimotor network(SEN),ventral attention network(VAN),frontoparietal network(FPN),default mode network(DMN)and visual network(VIS)regions were analyzed.Results(1)Motor function:there was no significant difference in FMA and FCA scores in three groups(P>0.05).(2)Whole brain functional connectivity and strength of homologous brain network functional connectivity:there was no sig-nificant difference in whole brain functional connectivity based on HbO2 and HbR in three groups(P>0.05).Compared with the normal group,there were significant differences in the strength of functional connectivity of the in the SEN and FPN regions of the HbO2-based homologous brain network in the severe group(P<0.05),but there were no significant differences in the regions of interest of the HbR-based homologous brain network in the three groups(P>0.05).(3)Functional connectivity strength of heterolo-gous brain networks:compared with the normal group,the functional connectivity of SEN-VAN,SEN-DMN,SEN-FPN,VAN-FPN and DMN-FPN in the severe group decreased significantly,and the differences were statistically significant(P<0.05).Com-pared with the mild to moderate group,the functional connectivity of SEN-DAN and SEN-FPN in the severe group decreased sig-nificantly,and the differences were statistically significant(P<0.05).There was no significant difference of strength of functional connectivity based on HbR in the three groups(P>0.05).(4)Correlation analysis between SEN-FPN heterologous functional con-nectivity and MMSE,FCA scores:MMSE score(r=0.32,P<0.05)and FCA score(r=0.38,P<0.05)were positively correlated with SEN-FPN functional connectivity.Conclusion The SEN-FPN functional connectivity may play an important role in the cogni-tive function of stroke patients.Altered functional connectivity patterns of SEN-FPN may be closely related to the occurrence and progression of PSCI,and changes in functional connectivity strength of SEN-FPN may be a potential imaging indicator of PSCI.