I need to make 2 intersection lines of my polyhedras to find the horizonline, how can I find it?

If the lines overlap with in tolerance, you should be able to use the *Intersect* commmand.

Several methods if the lines do not overlap within tolerance:

a) Work in the view which shows the line in the correct position relative to the object. Project the line to the object.

b) Work in the view which shows the line in the correct position relative to the object. Extrude the line to create a plane which intersects the object. Then use Intersect to find the intersection.