The goal of this clinical trial is to learn if high definition transcranial direct current stimulation (HD-tDCS) of right inferior frontal gyrus works to improve social impairments in children with autism spectrum disorder (ASD). It will also learn about the underlying brain mechanism. The main questions it aims to answer are: * Does HD-tDCS of right inferior frontal gyrus improve social impairments in children with ASD? * What are the underlying brain mechanisms by which the HD-tDCS of right inferior frontal gyrus improves social impairments in children with ASD? Researchers will compare participants received active HD-tDCS to controls received sham HD-tDCS (performed to mimic the sensation induced by real HD-tDCS before and after the stimulation) to see if HD-tDCS of right inferior frontal gyrus improves social impairments in children with ASD. Participants will: * Receive a dose of 2 mA HD-tDCS of right inferior frontal gyrus lasting for 10 days. * Receive social functioning assessment, functional near-infrared spectroscopy and electroencephalography measurement before and after stimulation * Visit the clinic once every 2 weeks for checkups and tests, a total of 2 times.