According to reference books and lecture notes, they mentioned that the two pi-orbitals of acetylene overlap and become a cylinder (donut) in shape so that the pi electrons can circulate along the C-C bond axis.(movement of e is not like the moving subject in macroscopic world. In the microscopic world, the electrons obery the Uncertainty Principle)

If we figure out the overlapping between these two pi-orbitals, because of the sign of each lobe, there should be a nodal plane in each new orbital after the interaction. Therefore, circulation of e- will be blocked.

So, how to explain the continuity of circulation of e-?

Is it the signs of orbitals can be ignored? But why?

using the charge density to describe the movement of the electron is better.

In an alkyne there is practically no barrier to rotation about the two C-C bonds at the termini, so the time-average of these orbitals ends up looking like a cylinder, while at any instant it would look like two orthogonal p-orbitals.

You can rotate those orbitals without changing the hybridization of the carbons in the alkyne, so there isn't any barrier.  I don't mean the whole molecule, just think about the pi-orbitals spinning around; nothing else has to change.