There are many popular digital piano, like:
1. Roland
2. Yamaha, and
3. Kawai
I want to ask about that brand comparison in digital piano (not Portable Piano).
How about its tonal, character, action, etc.?
And what is the best digital piano line from each brand?

Thank you

You cannot get an answer to that question. Because every user has his own favorite. There are also diffrent models for diffrent prices. All off these brands are known for good DP. Some prefer the sound of Yamaha, others of Roland etc.

Depends on what you want to do with a digital piano, what sort of sound you like, what kind of touch suits your needs, etc.

Please understand that the differences between portable piano and home piano are the furniture cabinet, the fixed pedals, and the speaker array. If those are your reasons to not want a 'portable', then it makes sense to exclude stage pianos. Otherwise, you should look at them as well.

You will easily find an answer to your tone comparison if you play samples from the three makers. All three have distinctly different tones. You will not find them to be the same. You will not like them all equally.

Touch is a little trickier. The three makers do not use the same action in each of their models, so you have to compare within one maker's products, not just between makers.

The second best thing you can do (the best is of course to audition the pianos yourself) is to link to the pianobuyer ad in the right column and access the free online edition. The writer of the digital section, Alden Skinner, is a member here. He presents invaluable information without bias. It's a very good primer.