The rootstock for all grafted Japanese maples is traditionally seedlings of the species, Acer palmatum. Root stock from Acer japonicum will work as well. I doubt Acer rubrum would be compatible but it might be worth experimenting with. If the graft took, you may be facing continuing vigorous sprouting from the understock, which will need to be attended to promptly.

Hi Gardengal48
Thank you so much
But I think it hard to sow the Acer palmatum seed right?
I tried too many time but I can't get a number of seedling.

Acer rubrum seedlings WILL NOT WORK as understock for Japanese Maples. Understock must be in the same genetic "family" (or SECTION) as the donor tree. In this case, members of the genetic Section PALMATA. Those species include:

Acer palmatum
Acer japonicum
Acer circinatum
Acer pseudosieboldianum
Acer shirasawanum
Acer sieboldianum

and a few more very rare species. The favorite understock plant by far is Acer palmatum. Some of the others, like Acer shirasawanum, have more fibrous stems and do not cut as cleanly as Acer palmatum. Others like Acer pseudosieboldianum do not have striaght, smooth stems; which is preferred for an understock plant.

You can order Acer palmatum understock from Pacific Coast Maples or from Heritage Seedlings.