["Autism Research, EarlyView. ", "\nABSTRACT\nAutistic children exhibit difficulties in audiovisual speech integration, which are associated with their social communication challenges. The neural mechanism underlying audiovisual speech integration difficulties in autism remains unclear. We recruited 19 neurotypical (NT) children and 29 autistic children. We recorded their behavioral responses and Electroencephalography (EEG) signals to audiovisual congruent syllables, and incongruent syllables that could evoke audiovisual speech integration (i.e., McGurk effect). For the EEG analysis, we further classified autistic children into the autistic McGurk group and the autistic non‐McGurk group based on their strength of audiovisual speech integration. Behaviorally, we found reduced audiovisual speech integration in autistic children. At the neural level, we found that: (1) NT children showed an early stage audiovisual processing (indexed by the N1 amplitude), which was altered in two autistic groups; (2) all three groups exhibited a successful audiovisual incongruence detection (i.e., phonological Mismatch Negativity, pMMN); (3) NT and autistic McGurk groups could successfully resolve the audiovisual incongruence (indexed by the restoration of pMMN), but the autistic non‐McGurk group could not (indexed by the sustained negative amplitude). Furthermore, we found a distinct temporal decoding pattern between non‐McGurk and congruent trials across groups: both NT and autistic McGurk groups exhibited early EEG decoding, whereas the autistic non‐McGurk group demonstrated successful decoding during late processing stages. Audiovisual speech integration entails a three‐stage process in NT children: early audiovisual processing, audiovisual incongruence detection, and audiovisual incongruence resolution. The altered early‐stage processing was possibly the neural mechanism underlying the reduced audiovisual speech integration in autistic children.\n"]