Is there anyway to combine these two solids?

You’re going to have to describe the problem you’re trying to solve.
I see an image of two separate objects.
“…combine these two solids”, is not enough detail to understand the problem.

I mean the left one
I have trouble boolean union those two
I want to make them as one single object

Than we will need the 3dm file.
An image doesn’t tell much in this case.

troubleshoot.3dm (203.7 KB)

Rhino’s intersectors are going to have trouble with that because of the converging edge curves and coincident surfaces.

I would recommend using the Intersect command between the two solids. Then use the result curves to manually Trim (or Split and Delete) the parts of the surfaces you don’t want to keep, then join the rest.

when i used intersect I got curves
is this the result that I suppose to have? and I could not find result curve command
Thank you for helping me out

Intersect creates the curves. They are preselected coming out of Intersect. Move them to a layer with a different color or change their color to something easy to see.
Next I’d Hide one polysurface and use the curves with the Trim command to clip away the portions of the surfaces that will end up inside the other.

Then Show the second polysurface and do the same thing.
Join the results.

Rhino isn’t going to be able to automatically do the Boolean so you have to, but creating the intersection curves, splitting the surfaces, deleting the interior parts, and Joining the exterior surfaces.
That’s what BooleanUnion does.