I notice that cable cannot pass a long distance (1000m), it's like this
Redstone I/O ------(1000m)------ computer, and the I/O cannot be detected even when the chunk of computer and io block is all loaded. So is there a limit? Is there any solution to this?

All the cables need to be chunkloaded for the connection to work at this time. As such, what you're trying to do won't work.

On 1.12.2, you can use McJty's XNet mod with the YNot addon as a workaround.

so if all the chunks are loaded, there's no such problem?

On 1.12.2, you can use McJty's XNet mod with the YNot addon as a workaround.

I would like to know if this would overcome the chunk loading problem?

1. If all the chunks are loaded, there should be no problem.
2. XNet's main feature is being able to connect blocks over long distances without loading all the chunks the cable is placed on. As such, it should work correctly with the YNot addon (which adds support for OpenComputers networks to be transmitted via XNet).

Worth keeping open; someone might want to tackle this one day.