After being informed about the study and potential risks, all patients giving written informed consent will undergo screening period to determine eligibility for study entry. Participants who meet the eligibility requirements will be randomized in a double-blind manner(participant and investigator) in a 1:1 ratio to probiotics PS128 group or placebo group. Each patient acts as his or her own control, and they receive both the study drug as well as the placebo. After a washout period, the participants will be switched throughout to different treatments（probiotics placebo group or PS128 group）.
The purpose of this study is to explore the role of probiotics PS128 in improving gastrointestinal dysfunction and core behavioral symptoms in children with ASD, and investigate the underlying etiological mechanisms of ASD.