<p>Molecular knots with topological chirality demonstrate superior spin selectivity compared to conventional chiral materials, exhibiting ultra-high spin polarization of nearly 90%, conductivity increased by two orders of magnitude and high-temperature stability (up to 350°C). However, the physical origin of this phenomenon remains elusive. We establish a fundamental theoretical framework for the chirality-induced spin selectivity in topologically chiral molecular knots and identify its essential conditions. Our calculations show that a single trefoil knot molecule exhibits spin polarization exceeding 60% along with significant conductivity, robustness unaffected by lattice reduction or structural strain. Importantly, when the topological knot degenerates into a trivial structure, accompanied by the transition from topological chirality to structural chirality, the spin polarization sharply declines, demonstrating a strong correlation between the ultrahigh spin polarization and the knot topology. This work elucidates the mechanism of spin selectivity in knot molecules and provides new design principles for future spintronic devices.</p>