Abstract: The research progress on the functional connectivity of autism spectrum disorder is illustrated. Autism spectrum disorder is an early-onset neurodevelopmental disorder characterized by the communication and social interaction impairments, repetitive and stereotyped behavior and restricted interests. The recent research finds that autistic adolescents and adults show the functional underconnectivity in the brain areas and this lower synchronization of neural activity has a negative correlation with the severity of symptoms in autism spectrum disorder. The functional near-infrared spectroscopy, a newly developed noninvasive optical neural imaging, is used to study autistic children between 8-11 years of age on the resting-state. The results indicate that, compared with typically developing children, autistic children show significantly lower functional connectivity in the bilateral inferior frontal cortices and temporal cortices. This functional underconnectivity has a negative correlation with the severity of language and communication and social interaction deficits of autism spectrum disorder. This study supports the feasibility and convenience of using the functional near-infrared spectroscopy method to assess atypical functional connectivity of cortical activity in autistic children and its potential for early diagnosis on autism spectrum disorder.