Pentaho

The trick may be that the JSON Input step is only available in a transformation, not in a job.

Try creating a Transformation rather than a Job and you'll find it right under the Input options under the Design tab (you can also enter JSON into the field next to the Steps label and the step tree will find the two entries for input or output of JSON).

I can search Json input and out from PDI 7.1 but not PDI 8.1

Are you definitely in the Design context for a Transformation and not a Job? I cannot tell for certain from your illustrations because my Chinese it's good enough and all I can see is that there are different step group headings. Here's what I see--but note that this is in a Transformation.

Perhaps try exporting one of your 7.1 transformations that use the JSON Input step and then import that transformation into 8.1. That should allow you to see the step in 8.1