1. Autism means not talking to anyone, and introversion means not talking to strangers.
An autistic child doesn't want to talk, even with his closest relatives, such as his best friend, his mother or grandparents who have been gentle with him. He will show resistance and escape.
And introverted, just shy, only to strangers, usually in front of familiar people, can still talk, just a few words, but certainly not without talking.
If parents are patient and gentle with their children at ordinary times and the children will never take the initiative to talk to you, then the child is autistic. If you are mean to your child, it is normal for him to be afraid of you at ordinary times.
Second, autistic children have no friends, while introverted children just have few friends.
Autistic children resist the whole world. Even children who are the same age, like-minded and friendly to themselves will not pay attention to it, or even take the initiative to stay away.
Introverts don't. They are just introverted, not so good at interpersonal communication, or some children are not so keen on interpersonal communication, but when their peers take the initiative to say hello, they will accept it, or they will take the initiative to choose people similar to themselves to make friends with others.
Third, autistic children behave mechanically, while introverted children do not.
Autistic children are lonely inside. They are troubled by their hearts, don't care about the outside world, and even slow to respond, because they are immersed in their own world, while introverted children are not. For example, if you call his name, autistic children may not consciously hear it, but introverted children will react, not necessarily verbally, but at least they will look at you.